The Battle: Are we extending life or prolonging death?

I'm sure this will be controversial to some, but our family is divided on this topic. Mom is 90. She was a very independent person, active in church, used to teach line dancing at senior centers, loved her sweets, loved doing family gatherings with lots of food, and loved the freedom of jumping in her car and going anywhere she wanted to go. That was 4 or so years ago. Diagnosed with dementia/Alz and can no longer drive. Has diabetes and can no longer have sweets, Cooking and eating are now basic limited and she gets no enjoyment from either. She has talked for more than a few years that she is ready to 'go home'. Her typical day is to go to mass every morning, after which she comes home and sits in her recliner. Gets up for lunch (usually a sandwich), then goes back to the recliner or goes to lay down, repeat at supper, and then to bed. She has several of us who are in and out, providing 24x7 care. One sister insists that we push to keep her "healthy", and closely monitors everything she eats and drinks. Another sister is more inclined to give her whatever she wants, but after years of this same routine, she rarely asks for anything different. Personally, I would prefer to tell her to forget all the rules and do whatever will give her some joy. Want Maple Nut goodies? Here is the bag, go for it! Want to go take a walk on the beach. Let's go! Want to turn on some music and dance? Big band or country! Bottom line, what is the purpose of life if not to live?