My roommate took my cup and I’m reaching my limit

I ended up getting an apartment for college this year with 5 other random girls. They’re nice, but it’s so many little things that have built up that at this point I’m so ready for my lease to end. One roommate in particular has done a lot of little things. Eating my Mac and cheese cups (I buy more expensive ones - the deluxe Kraft ones if you know what I mean), eating my entire loaf of bread in 3 days and leaving just the butts (I had none and SHE had her own loaf), so many other things, and now taking my actual things. We have a cabinet with cups in it. For our actual cups that we leave the house with (Hydroflasks, Owalas, or to-go cups) we DO NOT SHARE. like we all brought our own cups and use them. We have cups for in the room (without lids) we all share, but it’s a pretty clear difference.

The other day my one roommate walked into our shared poli-sci class (originally was super cool to find out we had the same major) with my one cup. It was a grad gift from a close family friend that I’ve been looking for for a while. Someone is ALWAYS using it and it’s never me. Like it gets clean after I leave for my first class and it’s taken by someone before I come back.

I made some comment to her in class like “Oh nice cup. I’ve been looking for it.” And she immediately got super defensive, saying things like “It’s the only travel cup we have” and “I’ve never even seen you use it.” I respond “yeah because everybody else is using my cup instead. I got if for my grad party and I feel like I never get to use it.” Class started and I left it alone and hoped I would see it in the cup cabinet again the next day.

Two days later (today) I asked roommate if she wanted to watch a show with a few of us. I knocked on the door and opened it when she said I could, and I saw her using my empty cup to hold up her phone as she watched a movie. I make another “nice cup” comment and she looked like she didn’t even care. Like clean my fucking cup and put it in the cabinet? I don’t use the cups that aren’t mine but if I do I clean them right away, which I feel like is common sense and common curtesy?

I’m really close to just going in her room and grabbing the cup and cleaning it while she’s out at this point. What should I do? I’m not super confrontational (honestly this is the most I’ve been about anything since move in at the start of summer).