OP I have only read the first half of the thread but I have read all your posts. My DD has AuDHD and has self harmed through the stress of school. She has been on medication she was 8 and has seen a psychologist regularly since about age 11.
She has missed a lot of school. At first I tried what many on this thread are suggesting - to get her in no matter what. Sometimes I'd be trying for 5 or 6 hours until giving up for the day. It was counterproductive and made things worse because she wasn't getting the day she needed to recharge in order to feel better and be more able to cope the next day, she was getting more stressed and more likely that we'd have the same battle again tomorrow. Her mental health plummeted and things just kept getting worse. Her psychologist advised me that if DD said she needed to be off, to let her, so that she could actually use the day to feel better. She also got DD to promise to try and go in whenever she could, as if she took too much time off it would create even more problems for her. This approach helped. Allowing those rest days did mean she was better able to function at other times.
Other things that helped were that if she was unsure about whether she could cope that day, promising that I'd pick her up if she needed me to, and doing it. We got an agreement with school that she could go to the office and ask them to phone me. The alternative was that she wouldn't be in school at all, so they agreed.
Lastly, working with the school and being absolutely honest with them meant that they agreed a part time timetable for her - initially dropping the subjects she wouldn't be doing at GCSE a year or 2 early. Then doing one less GCSE, and being allowed to have late starts and early finishes when she had no lesson on. If she needed a day off for MH I didn't need to lie. Working with both the school and the psychologist meant that we had an agreed, consistent approach.
This meant that although her attendance was low, she was in school for the important lessons. Building resilience in cases like my daughter and yours just isn't really a thing. It's about trying to get them through the day in one piece, and many posters on this thread won't understand that. It also has no bearing on whether she'll be able to hold down a job, because as you get older you are better able to control your environment. There are many different jobs and many different working environments. If you can't cope in an office you can do another type of job. My DD could not cope with with secondary school and needed those days off. It's not worth destroying a child's mental health and risking far worse consequences by forcing it. Her attendance in GCSE year was 30%, but a lot of it was sanctioned by the school, e.g. afternoons off when she had no lesson or PE. Arriving at break when she had no lesson first thing. She still got good GCSEs.
For A levels she attended far more because she chose 3 subjects she enjoyed, which really helped. Now she's at college and it's better again.
This was very long, I know, but I wanted you to know that you're not alone in going through this, that 'normal' strategies can actually make things worse and the best thing is to work with your DDs therapist and the school to find a way that she can manage and that helps her rather than makes things worse. And don't feel judged by people who don't understand.