You're doing the right thing by stepping back. You have to really.
My DD is year 10 so a year behind yours. She has ADHD and ASD and isn't coping at school and her attendance is very low. She's not academic at all.
I've been through (and I am still going through) all the stress and worry about her future options with, what is likely to be, no GCSE passes at all.
There's been a couple of very comforting threads on Mumsnet recently about those who left school with no exams. There were so many that returned to education, when they were emotionally ready, and did very well.
There were those that took a different direction through a trade or business that they enjoyed.
I'm having to reset my academic mindset and accept my DD is taking a different path to get to where she wants to finally be. She's very immature (despite thinking otherwise) and is simply not ready yet for what conventional life expects of her.
Has your daughter been diagnosed with any neuro diverse condition? Do you think the school avoidance is related to anything like anxiety or is she simply choosing not to go because she can?
As you said she's almost certainly going to make a hash of these exams. Set that as your expectation and hope it's the start of her resetting what she wants when she realises she hasn't achieved what she knows she can.
Once the exams are over the pressure of school attendance is off. College may be a better environment for her. If she has to start on a low level course to begin with then it's a stepping stone. If she gets a basic wage job then that's what she does until she is ready for more.
If she carries on as she is skipping classes and not caring, then you continue to step back until she's ready to do better.
I know it's incredibly hard though. The underlying worry all day every day never goes away. The sadness of the wasted opportunities is also always there.
The only person who can change it though is your daughter and at 16 this isn't it for the rest of her life. Education in her 20s or even 30s if needed is still right there for her.