Why is my mother so selfish?

Granted she lives with us but she has become more spacey, she had a car wreck and we still don’t know how it happened, possibly weaved off the road but it resulted in a concussion, broken femur, hairline fractures in the vertebrae and broken ribs and fractured sternum, plus blood trauma in her abdomen. While she recovered she increasingly became more stubborn, I even suffered a miscarriage and she barely responded at all. So then my role changed from daughter to caregiver. She’s type II diabetic and recovered from everything fine, no physical lasting effects and can’t remember what happened ( much less cares). Every day I have to tell her when to eat, she’s basically eating junk to keep her blood sugar number elevated barely. I cook for her then she doesn’t eat at all, like she’s being punished. She lies about checking her glucose numbers with her meter, will make a sandwich and walk off to do something else, always has an excuse about her attitude and behavior when I point it out or try to help her, since she lives with us she has no interest in her grandchildren and has a oh woe is me attitude. She has no bills apart from dr. bills, no longer drives, and she’s increasingly hateful, even when we try to help her. I repeat myself everyday and repeat my actions with her everyday, nothing helps. She would rather sit there and deal without and when her number drops and she starts talking out of her head she acts like it’s no big deal.