Is my mother being an enabler/codependent?

(NC)

My parents were married for over 25 years with my dad being an alcoholic. I realized that my mother was an enabler/codependent during their marriage. They finally divorced which my mother has always regretted believing she should have stayed with her man. Later she had another relationship with a man who was also an alcoholic.

My relationship with my mother has always been stormy and after I married she has had a very difficult time accepting my wife and kids. Things finally quieted down until a few years ago... My sister's husband abandoned her for other women and is now living off the grid in another state. My sister (51 years old) has deteriorated into the proverbial "cat lady" living in a home that is falling down without heat or hot water with her cats. She lives in filth with bags of trash and hordes food among other things. She doesn't work (never has) and was left with a mortgage payment.

My mother has become consumed about my sister's situation. She literally lives for nothing else but to worry about and help her. My mother (78 years old) lives on social security and uses every penny to try and keep my sister afloat. As a result her house is falling apart, her health is suffering (she won't even visit the doctor), and she is doing without food all to "save" my sister who refuses to get out of her mess.

My mother refuses help unless it's for my sister. She has turned on the rest of her family (another brother and his family) because we don't feel sorry for our sister. My sister has not had contact with the rest of us in many years.

This has been going on for over 4 years now. Is my mother being the codependent/enabler person in this situation? Can anything be done? If it keeps going the way it's going they will both end up homeless! Thanks for any advice you might have.