We are not young people. For some of us, our experiences with our aging parents are at the end of a long, unpleasant, and convoluted history with them. Explaining what we have experienced would take hours and hours and hours - or even a whole lifetime.
In the end, before they die, perhaps we struggle to grieve the person before us because we grieve that we have arrived at a place where we have to accept it was just never going to happen. That parent we wished for simply doesn't exist, and never will. They had no capacity to love their child, and they never will. That old woman that beat us because she hated her life, plain and simple, she's convinced herself no such thing ever happened.
It just is what it is.
If you are a person who needs to "do the right thing", then do that. Look to the places and people you can find who don't judge you, and will help you find the strength to get through it. And if you are the person who needs to walk away, the same, look to the people who don't judge you, and will help you understand your are not a bad person. Which ever you are, don't judge yourself. It was never about you, the child. It's about something we may never understand.
If you are a parent, look inside, if things are amiss. Some kids are pretty challenging. But if you are a parent, check in with yourself. Do what you can to ensure it won't be your kid writing this message some day, at the end of your life.
Caregiving has many challenges, especially if you have been mistreated in the past. I hear pain in your words.
Do you feel an obligation to care for your mother? Please know that you have the right to say to your mother that you do not want to continue to be her caregiver.
You can offer to help her find another solution for her needs.
Have you spoken with Council on Aging in your area to get an assessment of her needs and see what they recommend? Or a social worker to explain what options are available for her?
Wishing you peace.
Mutual respect, not demands, may get you what you need from your adult offspring.