Dear Kelly,
I am not a parent myself but I have been a difficult child myself. With us as children or teenagers, we don't want any advice (good or bad); we prefer burning our fingers and discovering ourselves that fire is hot. That's the general idea and I am sure you are aware of it.
On the other hand, I am not sure how good your own relationship and communication is with your daughter. In any case, you should objectively share your concern / view to her and the manner of speaking should be as if one friend/adult is speaking to another. Do not let her feel as if you are trying to steer the relationship for your daughter; rather put the idea there. And then she can decide on her own, your information might help her or may be she will come up to you for an advice herself.
It is a delicate situation and I hope that you are able to handle it carefully.