Mum has taken a set against my sister's husband who lives away - up till now it was a constant barrage about dad who died nearly 30 years ago - it is always derogatory and spiteful. She is 93, frail with dementia increasing - still lives at home with my sister who is still working full time, as a carer.
I think we forget our elders are people too. It is ok to tell them when they have crossed a line. For some reason people are in the mind set that they can never correct an elder.
I hope this helps. Don't forget to breath.
Will she be distracted into other conversations? Or just the one she wants to have? Probably over and over again.
Are these conversations on the phone or in person? Just thinking maybe in person you'd be able to distract with something to look at and talk about, like a picture? Maybe that's silly, but just trying to brainstorm.