This is very sad reading. You are trying so hard and you deserve to be supported. No-one should have to parent alone and I am sorry that you are having to.
I can relate to some of what you're saying as both my children have/have had big issues with anxiety, and at times I have felt hugely frustrated with them. But. That's my problem. My role is to support them, not to burden them with my problems.
I suspect that your daughter's anxiety is being compounded by your very clear frustration with her.
Here's the thing. Anxiety isn't a choice. You need to accept that else you really will drive yourself crazy. And once you accept it, that'll remove a big frustration for you, the idea that she is doing this deliberately.
You cannot punish or shame anxiety out of someone. That is very old-fashioned and harmful thinking.
My children have both been supported by child mental health services (with CBT) and by counselling services. One is doing much better down and is very mature about looking after her physical wellbeing and asking for help when she is struggling.
The other expresses their anxiety with anger and rudeness. It can be incredibly difficult. But here's the thing, ultimately I want them alive. Nothing matters more. I have stopped caring about attendance or results or any of that stuff. Every day is a standalone with some goals for moments of contentment.
I think so long as you take a combative approach with your daughter that you are both going to continue to suffer. You need to find a way to cope with your very strong feelings that does not impede her.
Let go of school marks. Imagine she was extremely unwell with a physical illness and what you would do to have her stay alive. I've been to two children's funerals this month and I don't wish the parents' grief upon anyone.