Notice how 100% of the warnings given to this younger sister were about money. As usual, literally nobody ever sat her down to explain the energy dynamics of being an introvert and how that is affected by having roommates.

Now she’s facing a situation she only has one way to deal with, without developing stress-related illnesses and mental health issues, and her sister is treating her with the same level of warmth and care as two strangers arguing over a fender bender.

YTA. Give your sister a couple hours to recharge. She’ll eventually get her own system for this worked out, but not if her legs are cut out from under her. She’s your sister not a goblin from another dimension.