QUESTION: Transferring My Girlfriends' Pokémon to Her Switch

Hey guys! I have a ton of my girlfriend’s childhood Pokémon in my HOME account. She doesn’t have HOME and doesn’t want to pay for it, but I want to clear up some space on mine.

The solution I foresee is to save-transfer her file of Shining Pearl over to my Switch (she has a cartridge I haven't played), move all her Pokémon over there (she never played anything past Gen IV, so it can serve as an unpaid storage facility in theory), then save-transfer the file back onto her Switch.

Will this work? Is there an easier or perhaps better way to do it? Thanks for any advice!