I came across this your girl on Saturday. Brooke Greenberg is a 16 year old girl that hasn't aged. This has baffled doctors and she is said to be unique. There is no other known cases like her.
This you tube video is long but the parents and sisters of Brooke are such a wonderful example of accepting their daughter/sister for who she is that I wanted to post it. Please if you don't have time now to watch it, come back when you do. It is a worthwhile watch.