Toxic friendships

I have this friend who no one at the school likes and she is really annoying and she also told me that if I loss 15 pounds maybe a guy will look at me and Im already self conscious enough. I don't want to be mean but I'm embrassed to be with her. I want to talk to the other girls and sit with them in class but she always follows me everywhere the only time I get to myself it when my other friend saying that she has an emergency. What do i do to get rid of her? She also likes to play alot of games and test me with things like she told her and her boyfriend broke up bc he liked me and he was going to ask me out and what I would say. I said I wouldn't date my friends exs then she said you passed the test. But I don't appreciate her testing me like that.