Some friends and i need to confront another friend about some issues, any good sites about interventions?

Question

A friend of mine has been dating this guy, and since she started dating him we have noticed major changes in her, in almost every way, none of them good. We care about her very much, and want to confront her in an intervention style format. We have some idea of how to do this, but we would like any additional help we can get. If anyone could provide good LEGITIMATE websites with information we can use, it would be GREATLY appreciated!!!!!!! thanks so much to anyone who answers.