If you'd asked me what to do before you got frustrated with your sister and expressed it, I would have encouraged you to be a bit gentler with her. The commentary about insanity and moving on was unnecessary. She's obviously very hurt (making irrational demands, yes; but in pain, too) and didn't need to be told anything that would make her feel worse about herself.
When Katrina, 60 (who withheld her last name for privacy), moved in with her family in Mexico during Covid, it made sense for her to manage her aging parents' medical care; she's a nurse. Her sister, who has an MBA, took care of the administrative tasks. It was the first time the family had all lived together since Katrina was in high school.
