As someone who is hypothyroid I can only imagine your poor dd felt awful. So pleased that she has been diagnosed and is responding well to her treatment. Be aware that she'll need regular blood tests and her medication adjusted as required.
My youngest dd was a really easy baby and a lovely child; then at 14 everything started to change. She became moody and sullen, difficult to get out of bed, grades dropping like a stone at school. Sounds like usual teenage behaviour but I was convinced that something was going on.
I went to school several times but they were no help just said she had to study harder.
She then started with stomach pains and missed school on several occasions without my consent. Eventually on the third time of taking her to the doctors they did some blood tests, it turns out that she has an underactive thyroid! She has been on tablets now or eight weeks and she is a different person happy and bouncy. So don't blame everything on teenage hormones sometimes they are just ill.