Most people act the way they do because the rest of us let them get away with it. True friendship is a valuable thing but not at the risk of the child. She's the most important thing in this. Sometimes as true friends we have to step up to the plate and get involved. Tell your friend about your concerns but do it letting her know it's out of love for her and her children. Tell her all you are asking is that she just think about the things you have said to her. Chances are she will. Most importantly I think you need to find some way to also talk to the daughter about your concerns for her. Being a teenager is a very difficult time in a persons life. They need all the advice they can get. It's a time in their lives when they can make some really big mistakes.