Passive Agressive sister?

I think my sister is passive agressive. She is staying with us for the holidays and has been acting weird towards me. She helps herself to my food and drinks (even when they are hidden in my room) (and lies about it usually). So I asked her to ask me next time she helped herself to something in the fridge that she didn't know who it belonged to, because she ended up drinking my boyfriend's tea and I had left it in the fridge for him. I said it really cautiously and not threatening because she is super sensitive. She said ok with this weird attitude and literally has not said a word to me since. (24 hours ago) I say little thing to her like hi, bye, thanks ,etc. She ignores them all and acts weird around me. I am getting this weird vibe from her. She does this every time I go out without her or do something she disapproves of. She is not good at hiding her discontent. What should I do? I am very upset that I feel unwelcome in my own home and my boundaries are being so violated. How do you deal with a passive aggressive person?