@workingtowards I am so sorry you are in this situation. And so sorry for your daughter.
Please, please look after yourself, ask for some counselling from your GP surgery, you need it.
I've got friends going through quite a few things and I haven't much advice except to say for the transgender thing just give your child lots of love and affirmation and go along with their feelings about themselves as long as you feel it is safe to do so. By that I mean I have a friend whose dd is identifying as boy, my friend was very shocked, handled it quite badly, couldn't cope at first and has slowly started to feel calmer.
Her dd is on the spectrum, and both the child and mum are lovely but the child is quite selfish and fixated and was very keen to get a binder. So the mum eventually got her a compression top from an autistic support organisation (PM me if you want to know more). All the other stuff like calling her him and using a male name and stuff the mum resisted and then slowly started to do it a bit of the time.
I think she feels that eventually this will either change or it won't and by the time her child is older she will find it has worked itself out! She's a very good friend and I have found it really hard watching her go through this but hopefully I've been able to support her.
I hope you have some friends who can support you.
My own dd is on the spectrum and has had some difficult behaviour, not what you are describe but sometimes difficult, aggressive etc and quite obsessive about certain things. When my dd is so diffiuclt I do rage at her dad and complain but eventually I know I need to just get on with things and make the connections where I can.
Another dear friend has a dd who self harms, but, and here is the good news, despite the self harm and mental health issues her dd is growing into a lovely woman who is looking to the future, work etc, relationships.
All these friends I have known for years and seeing things move on and get better has been quite inspirational. I can't promise that for anyone, of course, but things can get better.
Please get yourself some support.