Thank you! I'll find out who she's seeing - it's at UNC Chapel Hill. This was a second appointment and they took more blood and will be proceeding with estrogen patch if nothing else turns up. But this other possibility was mentioned... She's lean and long-legged, and at around 13 suddenly her feet grew to size 11, which I thought would mean she's going to be very tall, but she's not, so far. She's very stressed, and that seems to be one possible cause.
Used to do gymnastics until she got a lump on her wrist that's mysterious. Now she does acrobatics and cheerleading, of all things. I was surprised they didn't mention testing for celiac, but maybe that's not meaningful.