Folate is folic acid. Some people cannot process the synthetic form so getting folate as metafolin can help. (Natural form). (I've only just found this out, no idea if I'm one of them but it can't hurt and it's a b vitamin, which are water soluble so get flushed out of not needed).
20 is rubbish to be honest. I found it enlightening that when I saw the print out for my ferritin, the normal range was 70+. 50 is borderline, mine was around that and I found I was much better as soon as I hit that higher level. I think for many people it's not a huge issue so gps don't bother, but it really can make a difference. (I used to think this was all bollox till I experienced it myself, educated by the good mn ladies).
This might just be me, and I was having tummy issues caused by the iron I was taking, but I discovered by accident and the support of a great gp that cutting out milk made a huge difference to my iron levels.
I did drink it all day in cups of red bush tea, switching to coconut milk and now oatley made the difference of +30 points in only 5 weeks. We were trialling coming off the iron to see what the drop might be in one month, while I looked at ibs things, one of which was a loose FODMAPs diet. I didn't expect it to go up!
I hope your daughter feels better soon. I remember how shit it was.
It might help her to learn about celebs with thyroid issues and see them now - Hilary Clinton, Rachel from steps, I think Ellie Goulding had a thyroid issue of some sort. There are a few athletes too.