I'm an autistic parent to an autistic child with very different needs to me and this is something I struggle with a lot.
However, human contact and physical touch and comfort from a parent are very real needs that should be fulfilled and some children need significantly more than others.
It's been a huge source of guilt and stress and overwhelm for me and I've cried a lot about this. I am also the autistic child to an autistic parent who didn't cuddle me when I needed it, even though I needed it significantly less than my little boy, so I know the feeling of being rejected well.
We have laid the groundwork of teaching consent, with "that's my body and I've said no" or "that's my body and I am saying not right now".
Because as important as touch and comfort are to children letting them know they cannot cross people's boundaries especially if they are on the toucher side is very important too.
My little boy really looks forward to bedtime and morning time though as those 2 times are exclusively reserved for having big cuddles, for as long as it takes to sleep or to wake up steadily. Scheduling it in means that on the days where I am overwhelmed and dysregulated and struggling to stay on top of things he knows that he is loved.
If she understands the basics of disabilities you should explain mummy has a disability and it means sometimes she needs quiet, and no touching.
It could also help to wear a visual like the social battery badges, so she can see when you are open for cuddles and when you are not, and it reassures her that it's not her fault, and she's not responsible for fixing anything either.