Hi.
Sorry to hear about your old dog. One way to think about this is, you want her last days to be as good as they can. Only you know what is "good" for her.
Ultimately, I decided to let my last dog go when she was stricken with something probably curable with cage rest. I believed that having her spend two weeks crated up to return to a very frail state wasn't the right way to treat my old friend. Two years and one dog later, I am still sad and still convinced I did the right thing.