You shouldn't feel bad at all. When someone's quality of life is so poor, when they are miserable and uncomfortable or in pain, have just had enough and want it all to be over, why would anyone who loves them want their life prolonged?
I often wished my mother's life over well before it actually was. She'd had dementia for so many years and for her last few was a most pitiful wreck - doubly incontinent, not knowing any of her family, unable to hold any sort of conversation or take any interest in anything. Needless to,add, zero dignity or quality of life.
Luckily the situation never arose, but for at least her last couple of years her lovely care home staff had agreed with me that except in the case of e.g. another broken hip, there was to be no question of hospital. If Nature should finally be trying to let her go, so be it.