Jessica, I’m sorry to hear of your dd’s difficulties, and I can’t believe some of the previous responses.
Yes, of course parents should be involved in trying to ensure their dc are as comfortable and healthy as possible, but this needs to be in conjunction with schools. School has a huge part to play too.
I have a younger dd with ASD - she’s in year 7, so recently started secondary. At a not particularly selective girls independent school. I deliberately swerved the higher flying schools, as feared the pressure she could come under (she is bright, and gifted musically - she has a scholarship now, and could/would have done so at any potential school, which of course adds pressure in certain environments).
Her school has been utterly fantastic. She has high anxiety, and of course really struggled with starting a new school. Her form teacher has been amazing, taking time out each day to make sure dd is ok, and to check whether there are any queries or ongoing issues that need sorting out. For the whole of the first term, dd had a list of questions each day, some big, some small, most of which were outside form teachers area of expertise, but there was always an answer by the next morning at the latest.
Dd has been having some home issues, and there are a variety of options available to her. She can go and find her form teacher at any time during the day (even if form teacher is teaching a lesson), if she needs to talk. She can access the school counsellor. Dd has an older sibling with severe ASD, and can access a young carers group at school if she wishes.
There is a school mentor programme, and dd can ask to be paired with an older pupil if she would prefer to talk to someone nearer her age (and when she was really struggling initially, there were offers from older girls to help her out/be her mentor/look out for her around school).
I could not ask for anything more from her school, tbh. I am ‘lucky’ in that I knew dd needed this type of environment and so could choose accordingly, and I did disregard ‘better’ schools (ie those with more prestige) which I could have applied to, but I did not feel they would meet her needs.
I hope your dd continues to feel better now that she has dropped a subject. Easing some of the pressure must surely make a difference. And I hope she can access better support at school if she needs it - maybe the forced dropping of a subject will alert to the school that she really is struggling.