Take your time doing the application, read the requirements, just really have to prove that she is going to return back to thailand and has a reason to return, we got rejected first time we tryed, our fault ,did not follow every thing they required and should have included more information for them to be happy with. After this ,did the 5 year route visa for her to stay here and live with me. Now applying for citizenship as she been allowed to remain here for ever. If I did it any one can,people are lazy and can't be bothered to follow the rules,
Best to take your trousers or short off while attempting,this one of the 6 wonders of the world, takes years of practice, never attempt if you had a curry or very spice food.