Friend who is having an identity crisis.?

My best friend is encountering some issues with her identity. I don't really know if she knows that she is having the problem or not, but I can most certainly tell. In the past 4-6 months, she has been starting to cuss and hang out with people who have a bad influence on her. She was/is being raised in a Christian family and she loves God. Now cussing itself isn't really so bothersome to me (we all cuss sometime or another) unless its public and frequent, which is what this has turned into. Drugs, I know she isn't doing that. Sex, same deal. Lots of talk about it though. Alcohol, not so sure. Its VERY obvious to me that she is just trying to fit in.

Basically I think she is starting to turn sour from the sweet person that I used to know and love. I don't know exactly how to approach the subject. I wrote her a song a while back, I'm giving it to her this weekend for her birthday. Its about the situation that I see. But it seems like I need to talk to her more about the thing that I see happening.

In the town we live in, its pretty hard to find a friend who I can completely relate to and just hang out with. Not serious relationship, not awkward relationship- just friends being friends. So she is my bff and I really don't want her to end up where she shouldn't be. I don't know best for her, but I DO know that what she is doing isn't good for her. Please keep in mind that she's different. Not really the kind of person to get into cussing publicly and experimenting with things that she shouldn't.

I just need advice on how to approach the matter and what steps to take if maybe its not working. Its just not her personality to do what she is doing.