One of life's little ironies, more or less. If she were perfectly healthy and simply decided to stop eating, she'd probably be committed. It's a bit different for those we judge to be in bad shape, though - for them, we tend to let them decide for themselves whether or not they'd like to hang on.
It points up the misguided pity of those who want to put the disabled out of their misery like a cat that is too sick to go to the litter box any more.