What Causes Sudden Loss Of Weight After Beginning Of Periods?

My daughter has lost 11 kilos in 5 weeks time. She had a false diagnosis of anorexia originally. Now they think there is an organic cause. I just got her lab work and it shows her ALT is 193 (UK standards). Also her Thyroxine is 10.3 and T3 is 2.8. We have family history of thyroid problems and gut problems on both sides. She lost all of her weight really suddenly with no purging at all. This was right after her period first started. (then stopped). Can you advise us?