It depends on what stores are available in the immediate area of where your Mom's caregiver lives... Target or Walmart are good choices, if they are close by. Make it a store that has a lot of variety instead of a specialty store.
I cleaned houses for a lot of years and I got some pretty strange gifts during the holidays. I know that it seems more impersonal, but I can tell you that most of us would rather have cash.
CWillie, I know that some folk prefer cash, but the giver sees that as uncomfortable. The gift card makes us feel more comfortable some how. I would caution to give a gift card that can be used on daily things: gas, food, etc. working class folk do not appreciate a gift card to a book store or restaurant. We want useful cards to help us with our day to day. I am speaking from both sides of the equation as I have been a helper and I have been the person extending the gift card.