You have to apply in the UK for tourist visa. She needs a couple of legitimate reasons to return. I.e. House, kids, job (Proper job not massage or bar) She also needs to take a TB test in bangkok. Or youll have no chance. Oh and you need to prove your single, house owner and earn more than £38,600 per year. With evidence. Also...lol you need to prove your relationship is over 24 months with photos travel tickets etc. Good luck