Is she really a good friend?

[FaFa]

Ok well one of my good friends knows how much I like this boy, but lately she has been acting weird. She flirts with him and swings her hair when she is around him, and acts different. And my other friend told her that he liked preppy girls, so this past week she has been totally preppy...i dont understand it either. She has a boyfriend..why is she trying to steal the guy I have liked for so very long? And last week she told me that he liked this other girl, and when I told him that she said that he got really mad and said no way he would ever like this other girl. So she told me that, and made it all up...is she trying to get me not to like him? She knows I really like him too, and we are close friends. Her best friend tho also likes him (not as much as me) and she trys to get him with her too..but not with me. Whenever me and the guy i like are talking she comes and interupts us...im really getting irritated, what should I do? And what is she doing?!