Lesee if I understood you correctly. You mom is healthy enough to fly around the country, to get in fights with people, to demand money from relatives....
I dunno but it sounds to me like she is perfectly capable of taking care of herself when she wants to. Leukemia or not.
This was exactly what went through my head when I first read your post. Maybe it would help to remind yourself of all the things she IS doing for herself - like trying to find people to give her free rides in life, like using manipulative actions/words to attempt to get something for nothing. Seems like she's perfectly capable of taking care of herself - she just wants someone to blame her failings on. And she's chosen you (aren't you lucky).
For your part, you need to figure out how to not let her chose you. There are two parts to being "the chosen one". Part one is that someone(s) chose you, part two is that you accept being chosen. You can decline the position if you want.