Hi Nicola, your friends symptoms could one of many medical conditions. It's probably going to be a precess of elimination by her GP to rule some out.
Thyroid : my teenager was borderline with thyroid when she was just 7 years old ( her last year in Infant school and no medication). I was so concerned about her, but after the blood test results, our GP said it might fully develop when she is a teenager. Sometimes she appears to have symptoms, but not all the time, so I am on guard.
Take care RRB x