I have a very weird difficult relationship with my needy, manipulative, difficult sister - and after 25 years of this merry go round I have concluded that grey rocking, constantly redirecting to other resources, and having contact but only on my terms is the way to deal with her.
So if she calls, I don’t answer.
If she messages asking to chat I say I could do it in a few days - she of course then says she needs to talk now as she’s anxious/upset/whatever, and I reply that I’m sorry to hear she’s having a hard time and maybe she could contact x support service or one of her friends, as I won’t be available for a chat until the day I originally said.
In conversations I chat cheerfully about the kids, the dog, the weather etc and when she starts looping into one of her emotional spirals I do a sort of non-commital “hmm, that does sound hard. Have you discussed it with x support service?” and a calm “Well, no, I don’t think I can give you any advice on that, I’m not the expert, have you tried discussing it with y?” etc.
She has definitely noticed the change, complains a lot that I’m not as warm to her now, ropes in other relatives to complain - I always respond with variants of “I’ve spent a lot of time over the years trying to support her emotionally, but obviously I’m not able to give whatever she needs, so she really needs to talk to x support service” over and over.
When pushed I tend to remind people that I have a life of my own and limits to how much I can do, so she needs to talk to x.
So in your shoes first off I would find a local charity/service that offers support to elderly people especially elderly carers and then just keep referring her to that.
And I would do that totally guilt free btw. These services exist, you have no obligation to provide the services yourself just because she would prefer that - your own preferences get a vote too!