Dedicated cat lover here. I've gone to some pretty extreme (and costly) measures to bring my cat back to better health...but in this case, with a 17 year old cat who is clearly suffering and clearly near her end, it would be a kindness to help her pass with whatever dignity she has left. Without your help she may last a day, a month, or even a year, but eventually she will pass-- and her life will only get more agonizing.