I am probably going to agree here. Leaving an anon tip with crimestoppers is probably the way to go. I know you have been told to butt out - but what is going on is illegal, and now this poor girl has to live with the consequences of that. If her mother isnt going to protect her from herself - then someone has to!

On a small less important aside, it could also help your friend with custody issues of her baby.
100% agree with Inertia here. Report it for the friend and her child. There is no way I'd ever want my children near that situation.