My Thai wife and I took her Mother to UK in 2019, My Wife has been to UK 7 or 8 times, the appliction for the old girl was very similar to my Wife's application.
The mother is 74, Retired, Widowed, has savings in the Bank under 100,000b, lives in Buriram and was sucessful in her application, i think at that age UK Immigration must realise they're not going to disappear and hide away in the UK, & the Daughter ( my Mrs) has a good track record of returning to Thailand