Roommates are strange. I once lived with a dude in a wheelchair who would run his chair into the corners of the walls. He took a shit on my couch and left it in a bag, used to pour urinal piss onto the dirsty dishes.
Had another roomie after that who used to beat up homeless people, tried to beat up my boy at one point, too. They all started out normal, but eventually used excuses and diversion tactics to validate their strange actions. (I'm not trying to one up you with my stories here, only trying to point out that they started off doing overly dramatic stuff like your friend and it eventually escalated. People can become 'comfortable' acting like dickwads if they are allowed to get away with it the first time.)
Watch yourself there. If this chick is getting too wacky I would look to move out once the lease is up. Let her have her fun being a child and don't play in to it at all. People that get that extreme over small things can/possibly are, mentally ill and you should not have to deal with that.
This sounds like a very toxic friendship. None of the people that I know and consider to be my best friends would ever even dream of acting like this towards me. This is the sort of stuff we used to do to one another when we were ten, and not in our (almost in our) twenties. Get rid of this friend when you can and don't look back. You are not a punching bag for crazies. Good luck.