Hi Louis what’s she’s saying is correct: the UK visa people will only take any notice of money in her name in Thailand (not even a joint account will do). Whether you feel comfortable with the transaction is another question
next time try staying around Bang Tao / Surin - large expat community, beautiful beaches, great restaurants, most of us living here are very very happy and don’t want to leave for any reason
to the best of my understanding Airbnb / short term rental is not illegal in Phuket - I believe villas cannot have more than 4 bedrooms or rent to more than 20 guests per night
I thoroughly recommend Phuket - it rarely gets above 31 degrees, great air quality, most days with a nice breeze, and if you are looking for potential tourist income you would be amazed at the premiums tourists are willing to pay in the ~3 month high season