Hi Scampie
I am sorry your thirteen year old daughter is in so much pain, but I wouldn't give up.
I also suffered for many years with my knee, and doctors telling me nothing was wrong, long standing x-rays showed the extent of damage that was done to my knee, which has left me with Osteoarthritis.
But dont give up, keep on fighting for your daughter, I would go back to your GP and get him to refer your daughter to another Orthopaedic Surgeon for a second opinon, this is your right.
Good luck.
DeeDee