You can't be taken back to square one if you disengage and accept she is not going to be the mother you desperately want her to be.
You offer an inch, she takes a mile
So you stop offering inches
You stop offering anything at all. The conversation stays with the weather and what is in season, don't share anything that is important or your feelings if you are low contact. You don't respond very often to texts, drop the visits to 'rarely and very occasionally', become busy living your own life so you can unhook the clutches and think freely. She will notice and call you out, but you say "I did tell you I was going to be really busy Mum" and leave her to it.
Acceptance is key. She is not a good mother, she is not even a nice person, but that is okay, because she doesn't have to be anymore because you are an adult and can take care of yourself.
If you need to off load speak to a friend, get a good set of friends to help you move away more successfully if you haven't already. Have prepared answers for her demands. Plan birthdays and christmases well in advance so they are held on your terms. You can do this kindly and gently without drama, but don't count on her being happy with the new independent you, she is likely to become suddenly 'il'' or have a 'fall' or start to make ever more increasing dramatic reasons why you have to be at her beck and call. Same answer:
"sorry you are ill/had a fall etc, get well soon" do not restart the running around her again or you will be back to square one. You don't need to do anything with the information beyond well wishes.
Your self respect will return, your anger might also make an appearance when you think of the years you have wasted in servitude, and of course you may feel you have 'lost' your mother, but the truth is you didn't really have one in any real sense in the first place, it was always about her, and not about you.
I mother myself now, it is very lovely - I got the Mum I always wanted in roundabout sort of way! When I have a terrible day, I reassure myself tomorrow will be good and run a bath. I do all the things for myself that I imagine a good mother will do. I cry it out, make a cup of tea and a hot water bottle, I book spa treatments when I am low and girls nights, and tell myself I can do this, and I have lots of support from the inside. I am now responsible for me, and it took some getting used to, I stopped looking outside and started looking inside for what I need, and it was all there and will be for you too 