So, I go to a boarding school where we are randomly assigned dorm rooms and I happen to share a room with a girl from my main friendship group. My friend and I usually get along fine, we're not extremely close as she can be rather temperamental and I find I have to think a lot before saying anything "wrong" to her.
Anyway, in my group we always ask to borrow stuff from each other, sometimes outfits for a party etc. so I have no problem sharing with any of the 18 girls in my group, BUT this girl does not have any manners and takes my things without asking all the time. She uses my make up when I'm out and leaves it in a mess on my vanity, sometimes she keeps my things in her bags and under her pillow and I have to look for them after I realise they're gone. She wears my clothes without asking and leaves them on a pile on the floor and doesn't give them to the maid to wash.
This frustrates me an awful lot however I am not an angry person and I let things go, I remind her to ask me before taking my things and I wouldn't mind her using my things if she asked beforehand but shes so rude and doesn't take anyone's feelings into consideration. Today I had an argument with her bc she was going through my birthday presents and using some of the louboutin lipsticks I was given, which as usual she didn't put back. It has ended up with her storming out of the house and me crying bc I can't deal with her anymore, nobody in my group likes her much and if they knew that she'd made me cry she would end up with no friends as of today, so I don't want to tell my friends what has happened, I do however want to get through to her somehow.
Can anyone give me advice?
note: It's not possible for me to change rooms or to switch roommates, which is not something I'd ideally want anyway.