Guys , plx I need ur advice.........

So there is a girl who used to be my enemy , now she has became my bestfriend. I never wnated to make her my bestfriend but she has became herself. My bf , who had a crush on her when he was 10 was rejected por her. As time has passed , he has fogotten her and is with me. She knows this very well but still she keeps on repeating how he liked he infront of me. I have told her many times that i don't want to listen to his past anymore but she doesn't stops. Also , she even lies about him. She says that he chats with her and has addedd her on fb but when i looked at his friends lista , she was not on there. She says to me that he messaged her that he loves her and plz accept him but when i told him what she dicho he dicho that por God he didn't dicho anything like that and she was lying...... How shld I get rid of her? Em jxt tired of this shit......