Need info for a novel

I am writing a novel (or rather plotting it first!) and need your help, since I don't know much about foster care. One of the main characters will be a 17-year-old girl who is in a foster home since she was 15. She and her siblings were taken away from the violent/immature parents when she was 10, and she lived for 5 years in some foster care center (I don't know how that's called or how it works). She is a loner, doesn't get along with her foster family - or anybody else for that matter. She always feels "under attacK" and thinks there is a bad reason for anyone to approach her - she's suspicious and defensive like a hunted animal. Her new family is good and supportive, but the girl is too defensive to accept their love. Along the story she will mature and become a more open, happier person. Does this idea ring true? Are there any other facts that I should include? Any other traits for the girl and/or family, that often occur in real life? Is my character a stereotype or not at all? On the movie "White Orleander", that foster care center was a somehow unfriendly place to live - teens being competitive and agressive. In real life, is that true? Could it cause my character to become like I described her? Also, what is the difference between adoption vs. foster care? Can anyone explain it to me in a few words? Another: can my character decide to move out by herself, or does the law obligate her to stay with her foster parents? Any ideas or information would be much appreciated! Mileni