My teen daughter?

My daughter is 15yrs old and she is starting to change I fear for the worst. Her fav. color used to be blue but now it's changed to black ( no big deal) now all she wants to wear is black clothing. She's started listening to these bands: korn, avenged sevenfold, system of a down, greenday, kill hannah, and sum 41. I'm really worried about these bands could you please tell me if they have suicide lyrics or anything I should be concerned about? I'm really worried about her she's stopped hanging out with her old friends and now she has "new" friends that I hardly ever get to see. I've only got to see this one guy named Aaron who wears tight jeans which is really awkward to me he has TO ME longer than normal hair for a guy not like past the shoulder or anything but that's besides the point. Everytime I see him he is wearing these tight clothes. Should I be worried about my daugther please help me with this situation. Thanks, Judy.