What Should I Do?

The last few weeks have been crazy here. There is a girl that watches my son every couple weeks on the weekend. She is 13 and her mom supervises her because she has a lot to learn before doing it alone. I love this girl so much and I see so much of me in her. 
The problem is that I see a myriad of emotional abuse towards this girl going on when we are at her house. The adults living there constantly drag her down in front of people. She is so upset with how things are going in her home that she constantly wants to stay at my house or run away. For a while she wanted to get pregnant because, in my opinion, she wanted someone to love her unconditionally. She makes mistakes just like any other teen and while I agree that there needs to be discipline for these mistakes what I see is not discipline. It’s abuse!
I want to report the situation to the authorities but I’m afraid it will make the environment worse for her because they may not put her someplace else. I would adopt her if we had the ability to take care of another person. I want better for her but I also don’t want to loose her. She is such a sweet girl and she just needs to be loved. They say they do what they do because they love her but I really don’t see that as love. When I am around her house I can feel the negative energy.  
What oh what do I do???