Unruely mother

This may fall under "mental health issues" and "working through your frusterations and isolation". Hi. I am not the caregiver, my sister is at the moment and i am very far away from her and my mother. Neither of us have been in her life for a very long time due to resentment issues. But now that the time has come for somebody to step up to the plate to help her in her time of need, the rest of the siblings are either too busy with their own life or too far away. My sister has taken it upon herself to help because everyone else is making every excuse in the book to not help out. Her and i both have deep seated feelings about this woman for reasons i will not get into. For my sister to even consider trying to help her out is very hard for her. There are so many emotions that come to mind. With that being said. Our mother has stated several times that her children "owe her" to take care of her and is expecting my sister to move in with her although she has 2 jobs, 4 school age children, a home of their own. Just the other day while my sister was taking her grocery shopping, my sister asked her for her debit card to pay for her groceries, and my mothers reply was simply, " i thought you was paying for it". She continues to assert that (we) us children of hers, owes it to her to take care of her AND pay her expenses! My sister has already went above and beyond helping this woman and she is demanding her all out attention and being accusatory telling lies on her saying she forced her to move out of the nursing home she was in recently, which is not true. My sister has all but had it with her and i dont blame her one bit. Please if anyone can give some sound advice, i think we need an outside person to hear all of what is going on and to explain to our mother dear that she cannot be demanding any such thing of my sister or ANY of her children like that. Like i said my sister has about had it with her and is more than ready to wash her hands of her and not help her out any more. This is beyond irrational of our mother to even demand such from ANYONE let alone my sister!