Hey Phineas,
I know it's hard, damn hard, but you have to do this for you. Sure cancer and some other diseases seem to be the same, but it is not the same. She must choose to do this on her own, it is not our decision.
You are not abandoning her, you are choosing to protect yourself and in turn it will help her. They do not need us to clean up after them, they need us to let them fall down and let them pick themselves back up.
I realized this after cleaning up after my XAGF and even though she moved on to her next enabler, I still hear stories that ooze out of the woodwork of how even her new relationship is just a mirror to the all the problems we had in ours.
There are resources, but she has to seek which ones work for her. No matter how much we want them to get better, we come to the understanding that we are powerless to do anything.
Going to Al Anon where others had experienced the same things that I was going through is a big, big help. You realize you are not crazy! Coming to SR when I feel like it and hearing similar stories helps keep me strong.
When she decides in herself that she is done, she will be done. Not participating in her drama anymore, may show her it is time to be done. Give her the dignity to find it on her own, she is an adult. No more pitty, no more saving. If it is your HP's will, she will be back in your life, give her time and get yourself strong, so that you can make the best decision for you.