Sympathies! As pps have said, if she won’t have the help that’s offered, there’s nothing you can do. Please don’t let guilt lead you to run yourself ragged.
I have a similar thing with some very elderly, frail neighbours who often phone us in a tizz about something. What the wife has to do in the house - husband is unable to help - is just far too much for her now, and she often tells me tearfully that she needs help - but won’t let me do anything, except a few one-offs, and refuses to have the help her son tries to arrange for her!
She doesn’t want anyone coming into the house - ‘I can do it myself!’
It’s terribly frustrating. You can’t force anyone who’s still got all their marbles to accept anything.
We had this with an old aunt of dh, too, only in that case she just didn’t want to pay for help, although she could well afford to. When dh arranged help - and she did need it - she just sent them away. She wanted neighbours - and such as me, who lived a 2 hour drive away! - to do it ‘for love’. !!