Originally Posted by
EndGameNYC 
When I went to visit her when she was having symptoms, Mary Ann joked about having a brain tumor. On some level, and with her avoiding doctors for most of her adult life, she must have guessed that there was "something wrong." She also brought up, again, the idea of moving in with her last week. She lives alone in a house in Long Island. Given the events of the past several days, I'm starting to lean in that direction. We'll see.
That fits with what I imagined based on your descriptions. I was also going to mention this in my first post today: that from what you mentioned it sounds like she is the kind of person who does not only want to be "self-sufficient" regarding problems, but this independence comes with standing alone in her life in other ways as well -- since you did not mention her having children or a significant other, stuff like that. All this attitude and behavior will inevitably lead to someone feeling lonely and scared at times, especially when facing very difficult challenges that cannot be resolved simply by taking action and responsibility. Again, very familiar, not only from my own life but also from others close to me: my dad again, and I had an ex of whom your sister's story really reminded me of. The ex was a very strong character, always with "bigger than life" ideas and projects, super successful career, very independent and charismatic, always the kind of person who would go out of his way to protect the people in his circles, but denying a lot of his own needs and often the reality of his situation. Won't go into more details here but there was also a neurological issue involved that he did not take seriously enough. I hope your sister will. But again, I suggest that you guys not push her by telling her what to do...
As for moving in with her... well, give some time to that thought, it's really not the best moment to decide, I think.