This is the perfect time to be confrontational, because the longer you put off asking her about the stolen items, the worse it will get. Let her know that she’s welcome to borrow things, but she has to ask first. Then it’s up to you to say yes or no when she asks — say no a few times and she’ll stop asking. Many girls with sisters are used to borrowing from their sisters without asking and she might just assume that’s the norm. If talking to her doesn’t do the trick, then you should talk to your RA — no one deserves to live in the middle of a crime scen