A couple of things op.
I think you have to have a conversation with her along the lines of “how will coming home help?”
Obviously it will give her some financial respite, but ultimately, she is going to have to support herself financially.
She could have more emotional support at home, and structure, but it doesn’t sound like she is open to advice or to changing her routines?
As the parent of two YAs, one of whom with ASD, I would say that her moving in with you could just be enabling more of the same behaviour but without any of the natural consequences she is suffering now,
This sounds harsh but I don’t think it’s our job to make our twenty-eight year old adult child’s life more comfortable, even when YAs with autism often take longer to mature,
Comfort might be the worst thing for her atm. She may need to be outside of her comfort zone to learn and grow. And if it’s all a disaster, she might have to reconcile with her mum.
The only caveat I would say is, please try and put your scepticism about your sdd’s autism aside. It presents very differently in women as compared with the men. My dd with ASD did exceptionally well at school, as it was very structured, but she fell apart when she had to organise her own time at uni. She also found the sensory challenges of the workplace demanding; it was overwhelmingly loud, bright, distracting. Conversely, she needs the light on and to listen to a podcast in order to sleep.
These things may seem contradictory but they are fairly classic signs of ASD. For this reason, you have to be very careful about how you explain that you don’t want her living at home. This should be her dad’s task for a start. But it needs to be done very sensitively and couched in terms of what is best for her. Please don’t make her feel unwanted as people with ASD suffer with this all of their lives, making them extremely sensitive to rejection.
Instead I would offer to help her with her ASD. Is she formally diagnosed? Maybe you could help her with that instead? For my dd, diagnosis was very empowering bc it offered an explanation as to why she was finding life so difficult, it helped her develop strategies around it, and most importantly, it helped her find the right path of study and profession which took her ASD in to account. There will be a job out there that suits your sdd op, but she may need help finding it and moving forward to a new start.