Hi op, I'm in a different boat but I totally understand where you are coming from.
My son has very intense separation anxiety, but he's always had it. At nursery every single drop off was awful and it took him months and months to settle properly, with the help of some amazing staff and me and DH using lots of strategies at home.
He also started school in September and I can't tell you how worried I was. The last few weeks of nursery were, quite frankly, awful. I could barely get him there and even things like his "leaving party" and school stay and plays, which other parents got to enjoy as nice, exciting things, were just traumatising to be honest. At the gates of a school stay and play (where the parents stayed!) he was trying to run off, screaming "don't take me in that place" 😬
He spent weeks saying he didn't want to go to school, wanted to stay with me etc. We had meetings with the school in advance - made arrangements for him to be able to have his toy rabbit and wear his hat in school. They met with nursery and noted down the strategies that worked for helping him calm down etc. We tried his uniform on and did practice drop offs the week before. The first drop off was awful, as expected...
But he actually loves school! He cries at drop offs but not as badly as at nursery, he doesn't (for now) get super strong getting ready to go. We have to stick to the morning routine but he's so much calmer. At school they have a quiet room for when he goes in but the last few weeks he's just gone to "the book nook" and gathered himself for a few minutes. They have a set task he does first thing each morning to help him regulate. He seems to be thriving on the structure and routine of always knowing what is happening and where he's going each day. We are absolutely amazed, but not taking anything for granted!
I guess I'm saying, I've been there. It's really fucking hard and unless someone has been through it with their child, seeing the distress first hand, they won't get it.
I'd be cautious about getting into a habit of days off as it could be counter productive, breaking routine, making it less clear when she'll be in Vs at home etc. But, if she's that stres and exhausted, follow your instinct. Speak to the school, her teacher, the senco etc. There's a massive push for attendance now, but they need to see children as individuals not source data for their targets. They need to acknowledge her struggles and help you with a plan going forward to support her and help her thrive, however that may be.