Hey there, Simply put, this girl isn't a friend. A friend wouldn't spread lies like she has been doing. I think she is bad news and doesn't deserve your friendship. I think you should stay well clear from her. I know you don't like losing friends but would it be a great loss if it was someone that tells lies like that. Also, if they all know she is a liar and does these things, I don't understand why you'd want someone like that in your group. Personally, I think you'd all be better off without her.
I don't know why she would tell these lies. And there isn't much you can do if she tells them other than just block them out and ignore them. You know they aren't true and so does your friends. Don't allow her to ruin your relationship and friendships with these nasty lies.
I hope that helps. Good luck (: