my sister steals everything from me

i need advice on what to do to stop my sister (15) from stealing everything from me, nothing seems to work and i am so sick and tired of this situation. i have tried telling her even screaming at her to stop but she says sorry and keeps at it. it's unbearable. i am going to move out next fall, but it's annoying i can't leave my own stuff in the bathroom, in the dryer or in my room unlocked without her stealing it.