My gosh, Jane, what an incredibly tough situation for both you and your mother. My heart goes out to you both. As to when enough is enough, I guess that has to be her call. I cannot tell you what to expect if she declines further treatment, but I am sure her doctor can. Given the movement to prevent pain and suffering, at least you can be certain that drugs will be available to deal with pain. Let us know how you are both doing. You have friends here.
Joanna