Yes, there's an element of that and I can deal with that (and went through it all years ago with another family member, who complained about every aspect of her life but was then adamant that nothing could be changed; turned out that she enjoyed having a moan!). But what's a little different now is that there are two issues underlying mother's diatribes - how to cure her health problems and whether GS and I are doing enough to help.
I'm sure her general health and wellbeing has declined, but she's talking about some very specific health issues that have identifiable causes (and treatment options, which she refuses to access). My suggestions aren't wonderful, they're boringly obvious - if you have (as she does) a problem that needs a minor surgical procedure, the solution is to have that procedure (or not, as you choose) but nothing else will make it go away.
As for whether GS and I are doing enough, we're doing as much as we feel able to do, but my mother is totting up how many hours we spend with her and somehow getting the maths wrong. I don't want to repeat the detail of the conversation because it's too identifying, but the gist was that I only spend x hours with her a week when the actual figure is three times that.
So that's why I feel ground down. She's rude and nasty but, as I read on MN last night, you only get one mother. I'm trying to support her, but can't give her the support that she wants, because there aren't enough hours in the day and, even if they were, they couldn't fix problems that need medical intervention.