As the child of a selfish, unloving father who only cared about people for what they could do for him, I'm going to be blunt.
Your mother will never love you the way you want her to. She will never acknowledge all your efforts to help her. She will never say 'You've been a wonderful daughter to me. Thank you.' She will wring everything she can out of you and never thank you for it, and one day she will die and you will be left feeling empty and resentful and guilty.
Or you could make every effort to get to the place I eventually reached, where my father died and I let myself acknowledge the fact that I quite simply didn't care. If anything, it was a relief to know that those occasional twinges of guilt about the 'poor, lonely old man' wouldn't come again. NB, he wasn't a poor, lonely old man. He was a perfectly content man who rather liked the sympathy he got about his distant daughter.
Some people are just complete arseholes, and when they get old and ill, they don't magically turn into poor, deserving saints, but people tend to get sentimental over them, making it very difficult for the lifelong targets of their arseholery to detach and feel good about their decisions.
For your own sake, and for the sake of your husband and children - who did not sign up for martyrdom at the altar of this unpleasant woman - you need to find a way to detach. Not doing so is actually a sort of selfishness. You want to protect yourself from the feelings of guilt and shame that you know will come, so you're throwing your family under the bus to keep those emotions at bay. Who is more deserving of you time and energy? Your mother? Or your husband and children? You know perfectly well what you need to do - you just don't want to do it. Your time/money would be better spent on some therapy to help you detach.
Sorry if that sounds harsh. I've been through it in a more distant way - no caring responsibilties, just the knee-jerk guilt to deal with - and I know it's hard. But feeling bad about something doesn't justify sacrificing everyone else around you, and your own wellbeing.