I have this idea for the troubled fifteen year old. This fits her. What if she is having problems with wanting to kill herself and such? I have so many friends who are dealing with it. And I think it would be really good if we added a character like that in there. It would be really relatable to several girls I know.
Anxiety doesn't always begin "naturally". Sometimes it is the end result of years of abuse, whether it's mental/emotional or physical. Be gentle with people that have anxiety issues, you never know what their story is.