I have a friend in the same situation - totally bullied by an unreasonable, selfish mother. Still, she feels compelled (obligated?) to follow her mother's wishes and demands - as she sinks into anxiety/depression, with her own life ticking away. Sometimes, she loses it and shouts - hardly surprising. I tell her to put her foot down, before it's too late!
I have to listen to all the despair, frustration and anger caused by this daft arrangement - to both sides - and neither of them are happy. It's a ridiculous, sad, miserable existence, yet my friend won't concede that she can't cope - a matter of pride. Like her mother, she won't ask for help, won't make changes - or hand over the reins. She has a choice - but is the author of her own doom.
We don't have children so that they can be stressed, lonely and sad slaves later (looking after us) do we?
If we need help, we don't get to pick and choose who provides it. There's official arrangements, Attendance allowance funding, carers, cleaners etc., residential and in-home help available, after all.
Why is this situation so common? It doesn't even work very well. If you couldn't do the caring (maybe due to sickness, accident or full time work commitments) somebody else would have to step in. There is always a choice!