My dad was the flip side of your story, 99 and 11 months when he died and though the body was strong, the brain fell apart. I was very relieved when he died, his last two years (covid) were in a memory care unit and though he needed the care he also knew he was locked down and resented it. Take care of yourself and forgive any negative thoughts or feelings that you might have, you stuck by her at personal cost...many do not.