roommate issues pls help !!!!

okay!!! so my roommate has literally been such a brat these last few weeks and I'm honestly at my breaking point like idk what to even do. She's constantly eating the food that I buy, like I buy stuff that is low cal and more expensive because I like to have the most organic, best food when I actually eat and like she literally eats it all???? And then she had her sister come and visit and while I was at my boyfriends and I came home today and she let her sister sleep in my bed without asking????? And now she's all mad at me for no reason and like its so fucking annoying and idk what to do at this point like am I being a brat about this??