Relentlessness doesn’t mean “keep doing the same things you always did forever and get your fantasy life”. It means “pick one game, keep playing even when you have every reason to think you already lost the game, and you just might win it”.

No disrespect, I don’t want to diminish the utter torture that is chronic pain, but nothing you mentioned sounds like it’s preventing your SO from maintaining a posture of relentlessness every day until she dies.

It might not be what she wants, it would probably destroy her relationships and her mind, it would probably require her to do things that she abhors, but the door is still there.