How do I tell my friend she is gaining a bad reputation?

My friend is pretty much becoming a slut, , any word like that. She had with a guy she barely knew and now that other guys have found out they think they can get some easily. The worst part is I think some of them could get it easily from her if they wanted to. Also, she has a boyfriend and she is talking to another guy in another town (not just friends talking either) and also another guy who has a girlfriend. I've heard people call her a slut and stuff like that and me and another one of mine and her's friend are concerned she really is becoming one. I want to tell her but I just don't know how to without being harsh. I wanna tell her for her on good. What are ya'lls opinions on this and what I should do?