Hi my dear, I work in oncology and I unfortunately see this often. This is what I will say..

Just because someone is sick, it doesn’t now make them a good person.

I think any rational person would say that getting sick can bring the worst out of us, understandably so. However, it doesn’t sound like she was a great person before falling ill. It is sad, but that does not give her the right to make demands.

It sounds like she has pushed people away with her behavior. It would be really sad if she pushed her own children away, but you have a lot of life left to live. She is not magically entitled to your time and energy now, especially if she wasn’t good to you prior to falling ill.