I’m not hearing a lot of constructive suggestions from people who feel this is all ASD related and a ‘different’ approach is needed as to what that approach actually would be.
I don't think that's true. The problem is that you cannot lead the op step by step through a staged plan (which is likely to be a complex one) that might work using an online forum, not knowing the op's dd, nor whether op has consistently applied what might actually be the correct strategies in the past.
I've suggested utilising special interests (animals) as a hook and building up from there (to volunteering), incrementally. I've said that big changes involving volunteering or university are more likely to work by taking tiny steps towards those things, and suggested a staged way of doing that.
I've posted links to resources that have worked for many others, and many professionals are increasingly utilising, with demonstrable success. Has she tried low demand for 3 years without success, or has she tried her version of low demand which has resulted in no success?
I've tried to find out more about op's dd's likely responses in specific scenarios (such as providing very short, specific instructions relating to cooking a quick and easy family meal, like bunging pizzas in an oven) to understand more about the level of capacity, skill and motivation her dd actually has/ needs in a simple real world scenario.
And I've talked about anxiety medication (linking her engagement to something that intrinsically motivates her) to reduce the baseline enough to enable her to engage in proper therapy, supported by professionals.
The thing is, when parents of autistic children/ teens with lived experience suggest things that have worked for them, they're often told they're projecting, or met with disbelief that their approach has in fact worked, or that "well, that might work for your 9yo but we're talking about an adult here". Or, worse, told that their contributions are unhelpful and enabling, because the majority has decided that the op's daughter is choosing to behave this way, and so the usual behaviour management strategies apply.
I agree wholeheartedly that something has to change in op's approach and it's absolutely worth trying the things others have suggested on the basis that something else might be going on, besides the autism. But I'd like op to keep in mind the possibility that her daughter's world may shrink, rather than open up, to be prepared for that happening and to have a plan for if that happens. Because nothing cuts deeper than thinking/ knowing you've tried everything and run out of road. I'm thinking of the op's own mental health here.