AIW for not attending my sister's graduation?

Hello, I’ve (20 F) never posted on this sub before, so please forgive me for any mistakes I might make. I know that this is very long, so feel free to read the TDLR in the comments, but it really does give the full context I feel is needed.

Something happened recently that has made me wonder if I was truly in the right or if there are some changes I need to make. I’ve told many friends of mine the story and they’ve all agreed with me that I’m in the right, but I understand the bias that comes with that, so I wanted a neutral perspective.

About a month ago, my sister (24 F) had her graduation from university, which my parents and younger sister attended, but I didn’t. The week before, my sister had called me for a favor, asking me to drive to a city an hour away to grab a package for her that wasn’t delivered and give it to her when I came to her city for her graduation. I told her I would do it and a few days later told her I would only be free in the afternoon of Friday to do so, 5 pm specifically. She agreed with that time/date. The next morning, on a Thursday (the day before I was supposed to get the package) I found that she instead asked my mom, who was feeling unwell at the time, to get the package. When I learned, I didn’t want my mom to drive all the way for a package with the way she was feeling, so I told my mom to stay home and reiterated to my sister that I had already agreed to get her package at the time/date I mentioned, so she shouldn’t bother our mom. She again agreed and went about my day assuming I would be leaving tomorrow at the stated time to get the package.

I few hours later, at 5 p.m. on Thursday, she started spamming me with calls and texts asking me where I was in the middle of a work meeting. I responded, telling her that she either didn’t read my texts carefully or made a mistake, as I clearly stated that Friday at 5 would be the time I’d come for the package, not today, Thursday. She threw a fit, texting me that I was causing her problems and giving me an attitude as if I was the one who did something wrong. She then called my parents and demanded that they pick up the package instead, which they did. I don’t know the exact details, but my mom apparently yelled at her and also was upset at me over it. I was furious and because of this (and combined with the fact that I had work and two major exams on the day we’d need to leave for it, worrying me that I wouldn’t have time and wouldn’t do well on them if I had to speed through them) decided to not go to her graduation, which was the following weekend. My dad tried to convince me to go the next day, but I refused, stating I was busy anyway. My mom refused to talk to me for a while because of it, but we were able to make up after a week, even though I could tell my decision especially hurt her. My sister never apologzed or truly acknowledged the mistake and attitude.

Now I know what you’re thinking, “You’re going to miss a major one-time only event of a sibling over a mistake and some attitude? That’s ridiculous, dramatic, and stupid.” Honestly, if I heard this story from a friend with no other context, I would agree completely. I feel people should put small or moderate issues aside for major events, they only come once. However, there is so much more to this story than that which made me feel justified in my decision. Throughout our relationship, especially when my sister became a teenager, we never really were close or got along much. Simply put, we were really different people and our personalities clashed. About a year or two ago, I accepted our muted conversations and interactions as simply being two people that weren’t meant to be close, but still family that would be there for each other if something happened and wishing the best for each other.

However, recently, the general negative feelings I’ve had about her have reached extremes to a point where I don’t want a relationship with her at all because I genuinely find her to be a bad person, sister, and daughter. My sister and parents have always fought because of her tendencies, for example, she’s very money-oriented. Her whole teenage and young adult life was her getting significant amounts of money from my (not particularly well-off parents) for things like clothes, hair, makeup, vacations, etc. My father bought her a car as a teenager, which she totaled due to careless driving (she has a tendency to text while driving, multi-task, and drive over the speed limit.) When he bought her another car, she did the exact same thing. These crashes really damaged my dad’s insurance, as he was dropped from a good provider, and had to pay significantly higher rates, something that always stressed him out.

I also find her to be very selfish, only speaking to me and my parents when she wanted something, like money or favors. She only visits or talks to us when it's convenient for her, and expects most people to change anything or everything (schedules, plans, accommodations, etc.) to suit her needs on a whim. I’ve never been able to have a good, worthwhile conversation with her, because the few times we spoke that weren’t requests for something were always rare rants from her about some personal issues or lecturing me with values that I don’t agree with and she knows I don't agree with (for example, she states that you should only be friends with people that will offer you something, like connections or resources, or that men should treat women like queens and that women are the prizes, which are concepts I don’t agree with, but she's free to have these opinions, I just want to be left alone.)

She’s always complained that I never speak to her about my problems or life and stuff, but she doesn’t realize that I gave up on doing that a long time ago, because I realized that the times I tried to come to her for advice or just a caring ear, she would make me feel worse, making me feel as though my issues were always my fault, emphasizing my insecurities as the fault (I’m a pretty quiet individual and dress in a way she doesn’t like), not offering any supporting words, or quickly changing the subject to be about herself. For example, I reached out to her once to try and get some support and advice over an issue; I felt really lonely and isolated at my university that I was still pretty new to. Instead of comforting me reminding me I'm not alone or something, or kindly recommending me to try and join a club or speak out more, she instead said I was just imagining it, that I dressed and spoke in weird way so, of course, people didn't want to interact with me, and then basically ignored me saying "I don't know what you want me to say," changing the subject to something about herself.

She’s also had a long-running habit of making me feel bad about myself at random, as whenever she’d see me, she’d make comments about how my clothes/hairstyle were ugly and needing to be changed, grabbing my hair and trying to force me to change, or that my hobbies/way of speaking/and more were weird and problematic (it made me so insecure, I was genuinely thinking she was right and asked around to different people and learned no one felt that way, my biggest issue was that I was quiet and kept to myself. I have a fiancee' and many close friends who are just like me when it comes to mannerisms and hobbies.) She’s also never followed through on anything, she always comment that we should hang out or that she’d come visit my apartment when I invited her or we’d do some activity, for which I would actually be excited for, even planning a date/time, and then she’d just never show up or follow through, not even giving a text mentioning it, pretending like it never happened. (Note: I would always visit her with my parents when the opportunity arose, as she lives hours away.)

I’ve always felt subhuman to her, just a prop to benefit her and someone who should drop everything and change anything/everything for her sake. Simply put, I don’t feel ever genuinely cared for by her. I also find her to be a major hypocrite, always lecturing me on being active in our cultural/religious community, being a devout Muslim, etc (I've never been the most interested or active in my culture or religion, as I just feel disconnected to it and want to invest my time in other things.) However, she does things that are the complete opposite of what she preaches, going to parties with alcohol and more, not praying, she’s admitted to smoking hookah and drinking, and wearing extremely revealing outfits and posting images to hundreds of thousands on social media (If she wants to live that kind of life, that’s her business, I don’t care. My issue is the hypocrisy and her bothering my life decisions using religion as a justification to judge and hound me and feel self-righteous.) 

One of the biggest issues about her appeared a few months ago. It’s related to the fact that my sister is someone who is determined to appear rich and flaunt an ideal lifestyle (she has hundreds of expensive outfits, takes pictures of expensive vacations and activities, tons of gold and diamond jewelry pieces, buying food/eating out at expensive places, etc.) when it comes to social media and friends/family/etc., despite not actually being rich and being heavily in debt, always crying and complaining that she's broke and needs help. Before I was an adult, my sister acted as my dad’s translator and supporter when it came to legal documents, financial stuff, etc. as English is his second language (I currently help my parents with this kind of stuff since I’m nearby). My dad mentioned to me that he was getting called by a certain credit card company that he was late on his card payment, but that he wasn’t aware of this account or being late on anything. I called the company for him and we learned that my sister used my dad’s ignorance to create not one, but two credit card accounts under his name (making him solely responsible for the debt), each with about $10,000 in debt. My dad was aware she had one (not two) accounts with this company, but was told by her that he was simply a co-signer, and that she was also on the account, but the truth was that there were two of these accounts, with her name nowhere on them. While I don’t know the exact details, to my knowledge, this total $20,000 debt wasn’t for necessities (school or business; btw, she has a business that she pressured my dad into being a cosigner for, which he regrets immensely, a business which is currently having some major issues from what she’s told me) but for things such as her trips and clothes and such.

My dad was furious, and when he called her to confront her about it, she lost her mind screaming and crying that it wasn’t her fault, she had “so much to deal with,” and that “he owed it to her to help pay off this debt because he never helped her.” My dad has financially helped her whole life, paying for expenses like insurance long after she moved out, got married (I have no idea what her husband does and doesn’t know about her), and started her business. This is something that increased the resentment I felt toward her as from when I was 14 I would give my parents half of each paycheck to help them, save up for my own car, and pay any big expenses related to me, while having to use the rest of my paycheck to pay for general expenses (cleaning products, gas, etc,), making me feel like she was always getting away with stuff I never could and getting special treatment. Going back to the debt, my dad was extremely stressed and just shocked, caving into her screams, and is currently still helping her pay off this debt. My parents acknowledge all of her issues and bad tendencies, but still always try and get me to speak and be close to her because “she’s your sister, she’s family, family is always the most important.”

Normally, when we’d have a fight or an issue, my parents would make us apologize to each other, hug, and make up, then continue like normal, but a few months before the package incident was the first time I refused to repeat the cycle. My sister had visited my parents and I did as well, but we had an argument because she did this thing that she does to me which really eats at me because it legitimately makes me question my sanity sometimes that she's been doing for years, where she turns my parents against me and makes them (and sometimes me) think there’s something wrong with me for having normal behaviors/reactions, gaslighting me into thinking I’m mentally ill. To help you visualize what she does, it’s like she slaps me hard in front of everyone, then when I understandably get annoyed, angry, or sad, she says things like “Are you okay? This isn’t normal. Do you need a doctor, do you need help?” while laughing and giving expressions to my parents and others, convincing them that I’m being weird and making me feel crazy. She did that again with my parents and I was so sick of it. I snapped, told my parents goodbye, and left, then refused to speak with her for the first time. A few months later, my parents convinced me to come with them to visit her, I was cold to her and then my parents made us make up like usual, where she went “I’ll be the bigger person, as always, I’m sorry.” and then hugged me. She’s always down to hug, apologize, compliment, and more in front of my parents, her husband, and others, but when we’re alone, it’s like a complete personality shift where she barely talks to me, makes fun of me, and gaslights me.

I do want to admit some things to try that might be relevant and get unbiased feedback; 1. I rarely apologize first, because I genuinely feel I haven’t done anything wrong in our issues, but of course, I could be wrong. 2. Because of my quiet and introvert-kind-of personality, I tend to have issues with tone and expressions that can make it seem like I’m feeling one way (negative) when I’m feeling another (positive, neutral.) I’ve tried to communicate this issue to people, including my sister, but I understand the way this can make people feel when interacting with me and making assumptions. 3. I had an issue of being overly sensitive and emotional when I was a teenager, but I've acknowledged this major flaw and genuinely feel like I have overcome this as I've come out of my teen years and learned to take dissenting opinions, jokes, and critiques, but my family is now used to this personality, so I feel like they tend to assume I’m the same and not take my concerns seriously. 4. I wasn’t as active in inviting and planning interactions with my sister as she was or seemed. My reasoning was that she would flake like usual or that I wouldn’t enjoy spending time with her anyway due to how she treats me, but that was/is still an issue of mine. 5. My sister has had her own significant issues being the oldest sibling who had to handle a lot of responsibilities and high expectations from my parents, with them mellowing out a bit more with me, and being a lot more lenient on my youngest sister, so I’m sure she has unique issues I don’t understand and has a level of resentment toward me and my parents. There are many things I don't know about her because we don't talk, so it's possible there are many or some major issues that might explain her behavior or give important information. I've tried to speak with her multiple times about how I feel and the issues in the relationship, but it's always the same where she refuses to let me speak or acknowledge anything I say without immediately interrupting and fighting me. 6. My parents, while they've definitely changed so much for the better in recent years, were very strict, aggressive, and, simply put, weren't the best parents when my sister and I were younger, which definitely contributed to both of our issues.

Returning to the main issue, after the package incident, I exploded on my parents that I was done talking to her and explained how I felt about her, and then ignored her for the next couple of months. My mom commented that my sister was really upset that I wasn’t at the graduation. Afterwards, despite them always usually bringing her up to me and trying to get me to talk to her when we have issues, they were surprisingly pretty quiet about her, barely bringing her up to me. I noticed my dad especially seemed to not talk to her at all and grumble about her the rare times she was brought up, as if he’s exhausted of her. After a while, a few days ago, I received a long text from her, saying that she would never forgive me for this, that I was dramatic and sensitive and tried so hard with me, that she hoped I would have to tackle adversity some day, and ended off saying she’d pray for me. Reading it, of course it hurt me, but I also couldn’t help but feel like it was almost hysterical, littered with emojis that didn’t feel appropriate for the tone and other weird traits. I decided to show it to my fiancee’ without telling him the sender and asked his opinion to get an unbiased response, as he knows my feelings about my sister, and he felt the same, that it was somewhat deranged and was littered with logical inaccuracies with real-life events and its own words/logic in the text. He mentioned that he felt like it was written by someone who was detached from reality.

I felt guilty reading it though and it keeps popping up in my head even when I try to ignore it. I'm wondering if I made the right decision. This guilt, coupled with my parents still believing that I was in the wrong, made me want an outside perspective. I know this is very long and maybe isn’t very organized, but I would really want some feedback to know if I was wrong about anything. I'll try to answer any questions or offer any additional info needed. I truly appreciate it. 

EDIT: Hello everyone, thank you for the support. I wanted to clarify something when reading some of the comments. I think many people misunderstood the slap part, my sister never slapped me, I was using that as an analogy for how she'd treat me as it would be easier to visualize than mentioning a specific comment she would make.