Welcome back Ettie. Very sorry to hear that about your mom, she's very lucky to have you and your family there to care for her in such dire straits.
Regarding your question, I really don't think there's anything you can do or say that will change her motivation to quit. She will need to do that on her own. You can certainly be there to offer support if she asks, but there's no was you can "fix" her. Taking care of yourself and getting support for the damage she's done to you is important too..have you considered al-anon by chance?