Why?

I'm really disappointed. I got news about one of the girls that went to the school where I worked last year. This was a child that I really enjoyed working with. She had some problems but nothing that was too major. I really thought she was going to make it.
This young lady reminded me in so many ways of myself. I could hear what she was going to say or know how she was going to respond before any words came out of her mouth. This young lady has so much potential. She's bright, all advanced classes but life has thrown here more than enough curve balls.
She had the chance to be adopted last year and the family changed their mind. She went back into foster care and then another family wanted to adopt her. She went to live with them and things seemed to be going well. Her grades were staying up and she was making more friends. When I called the school, they always let me talk to her and she always sounded happy.
What went wrong? A couple of weeks ago, she decided that she no longer wanted to stay with the family. She could give no real reason.
I think it was fear. The fear of loving and to be loved. What if she opened up her heart and let them in and they let her down? What if she got hurt again? What if they rejected her? So many what ifs.
I've known all of these what ifs and still they challenge me. I have to constantly consciously think about how to handle different relationships. I tend to want to run before letting anyone too close. I don't want to be let down, hurt or rejected. I still keep a sort of wall around me that few people are allowed to penetrate.
But, the older I've gotten, I've learned that some of these things are out of our control. You can keep people out, but you still will get hurt.
But, to a teenage girl, that thought isn't a reality. The number one priorities are self-protection and self-preservation.
I wonder why adults can't see the why of her actions. Why didn't they fight harder? She has now been moved to another family and removed from the school. Will this child be lost to just repeat the cycle of what landed her in the system in the first place?