People talking behind other peoples' back to say to other people that people are talking behind your back who tell you then that other people, who talk behind others' people back, that they talk about you behind your back.
Meh. Waste of time, really.
I wouldn't put too much value into what other people say about what other people say about what other people say. Trust your own instincts and only believe your own first hand experience.
Tell your friend you don't like gossipping. If the girl has something to say to you, she will, sooner or later; if she truly dislikes you, it's in her best interest to tell you that asap.
Gossipping=trouble. Make it clear that you're not into that. For all you know, it's the people who accuse others to have said this or that who are being double faced or playing ugly games.
Apart from some rare exceptions, my experience with such gossips is that most of the time it's those who gossip that are the rotten apples, in this case, your friend and the girls' friend.