She thinks i am jealous of her. . . . Why ?

here goes. . My ex-roommate and me are clmates. She is a bad looker according to everyone else, gets poorer grades than me though is a lot more hardworking and is not as affluent as i am. She was in the habit of picking up my things without asking me and i tolerated it quietly for a long time. However, i couldn't take it and told her last time that i don't like it. She got annoyed, said that i am narrow minded and changed her room right after. But before that, she went around telling everyone that she is the prettiest girl in college and that i am jealous of it. She screamed at me saying the same thing and told that i am a psycho before leaving. Am still not being able to understand her reaction because i get compliments for my looks everyday when she is particularly bad looking. I am not even insecure about the way i look. Why did she do that ???