If she comes here and overstays, when she gets caught she will presumably be deported and will never be allowed back again. You can’t want that.
Surely it would be better to continue letting her come for the duration of the six month visa and return home? Perhaps with a family member for a month or two if jobs/funds would allow?
Is it just your family that’s left, are their any more if her children still alive, even if in other foreign countries to your own? If there were then that could mean more regular visits to her if their jobs/funds would allow?
Many must be in the same position.
And while the nhs used to fund treatment for all, I would assume that this will be tightened up in future after Brexit ans the impact of covid debt.
So invoices will need paid for A&E visits or whatever, so you can’t rely on that. Imagine how awful it would be to know she needs x amount of treatment costing say £3k here, but at home it would only be £500 for the same treatment. It would have been easier to find the money to fund her treatment in her home country.
An awful situation for all concerned. Especially if it’s cancer or something and you just can’t find the £20k or something to pay for it. But if she was at her home it would be much more affordable?
I hope you get something sorted, what a nightmare.