When my mother in law, who was a complex, intelligent person but a terrible mother, developed dementia, we took care of her as well as she could possibly be taken care of, not for her sake but for the sake of the voice in my husband's head that would echo her words to him in childhood. We can tell that voice, "he was a better son than she ever was a mother"
Interestingly the more she declined, the better she was to him. It doesn't negate the harm she did when he was a kid, but he walked away from her death knowing he'd done his best.
It helped that we inherited a fair amount of money from her but it wasn't why we did it.
This does not mean you are obligated to take care of people who were awful to you, but breaking the cycle on purpose is good, whatever that looks like.
Human beings deserve care, even if we don't like them. No one deserves abuse.
And if a chance for compassion and seeing the complexity of a person and finding some peace in their old age is possible, that is better for you in the long run than holding your fury longer than you need it.
We could have made her miserable. She probably deserved him walking away. But he deserves knowing that he is so much better a person, as both a parent and a child, than she ever knew how to be.
