When I was staying at my mother-in-laws I used the 'away from home and all the things I had to do' time to go through her old photo albums with her and make sure that I had made notes on who they all were.
She enjoyed talking about the past - she could hardly get out of her chair so it was that or watching Sesame street (which amused her), or listening to music from the past (most of the night).
And now she is not here to ask I know who the pictures are. With my parents albums it is guess work.

I also second the need for time to care for yourself. It may seem unfeeling to enjoy yourself when someone close is suffering, but getting depressed yourself will not help her.