Being a parent/sister

So, a couple of years ago my husbands father passed away. He left my hubby and his brother (both in their 30s) and a little girl who was 14 at the time. She is of course their sister....and mine now through marriage. My husband nad I tried to take over the bi weekly visits that she had had with her dad. Mainly to try to keep consistancy in her life, but also seflishly so that we could spend time with her and she could see the family. Well she turned 15 and things starting getting crazy as they normally do with teenaged girls. Then she started talking to older men, lost her virginity to someone that she had dated for a month, and started sneaking out of her mom's house. This year her step father died. She got her drivers license. And had CHANGED immensly! Lying to everyone, breaking promises. Well, I finally informed her mother of a few things that I knew had been going on. I was trying to be a friend, and finally realized...NO when she is around I have to be a PARENT! I will always be my kids' friends (In fact my 17 year old's friends say we are pretty awesome), but I will always ensure they are safe....ALWAYS!