She's been living with my sister and I every other month for the past 13 yrs. Although, she just started paying $500 a month the past 3 yrs. We do everything for her. Meds, food, bathing, doctor visits, laundry, etc. She can't be left alone, so it's 24 hour care. We feel she should be paying more. It was difficult to just get her to agree on the $500. How should we approach this? We have 2 other siblings that aren't able to care for her.