Thank you for all your replies. As said before, reading them makes me feel so much better as I've been harbouring difficult feelings towards my mum for a long time and the cumulative effect is getting hard to manage. Thank you ASDMommyASDKid, the theory of mind explanation is spot on.
In a way I feel twice a bad now because with men in my life I did exactly what my mum keeps doing with me, not seeing them, always projecting myself and wishes on them, and no surprise they run for the hills and I felt utterly devastated when they did and unable to see what I did wrong.
The good thing is that I've finally learnt and I can now connect in a more healthy way with people and "read" and understand them, but having to be reacquainted every time I visit her with her projections and inability to understand me reminds me of the painful experiences I had with men and how I smothered them (I always fell for avoidant Aspie men where I was the anxious/needy one, so a recipe for disaster).
As for the calls, no she would not write, she has trouble writing as she didn't go to school for very long, it's not something she'd ever contemplating, it takes her some time just to write a simple note. Telling her I can only talk once a month would upset her a lot, so not sure I can do that. Restricting the time to 10 minutes a week might be the only option.
And yes I try and go to the library and shops on my own when out there so I can get away for a couple of hours.
As for my sister, she thinks my mum is very selfish but she is the dutyful daughter who will do what is right and act properly towards her parents regardless. She has her own family, is married to an Aspie man and has an Aspie daughter she's having lots of trouble with at the moment so my mum doesn't sit high in her agenda at the moment. She did go through a time of severe anger and hatred towards her recently, which I think is still there to some extent, she's had some therapy and realised my mother was never a mother in the true sense of the word to her or to me. She's ten years older than me and basically had to play a motherly role in my family, my mum abdicated her role and my sister became in effect truly the mother to both me and my mum up to her getting married.