back in the UK

Hello. I'm looking for some advice on a tourist visa application for my Thai wifes mum to visit the UK this summer. Ive done several tourist visas for my wife and also just done the eextension to the UK spouse visa. However I imagine there is a different approach needed for the mum as we need to prove she's not going to stay for ever etc. Can anyone with experience of this give me a hand. She is retired so no job to guarantee her so im just wondering if its going to be possible or not. Thanks Back in the UK