Mom frequently says "I am just too old". How do I respond?

I amend my answer after re-reading the question. Please look into a memory care center for your aunt, at 92, I think mama deserves not to be a caretaker for her 88 sister who has dementia. I'm not suggesting that YOU should be the caregiver, either. You live a 100 miles away and probably have a family and that would be too much to ask. But perhaps having them in AL or progressive care facility would be the best for both of them and you!

Is she otherwise healthy? Being 92 and live with a sister that has dementia? Oh my, no wonder she is tired! I do hope she is not the caregiver, that would be way too much for her to handle. Could you let us know what the living situation is? Are they in AL? I know at 59 being a caregiver is hard and tiring, it would be impossible for me at 92! Give her a big hug and please let us know if they are under care or going it mostly alone (with you helping, of course).

I would tell her " If you are still here, that means God has work here for you to do, so ask Him what it is. God has a plan." and "Maybe God knows I still need you here, for a little bit longer, OK?"