You would find it very difficult to obtain a visa for any Thai lady to come to UK, to live, very difficult even for a short holiday, too much red tape, takes months of preparation and a helluva lot of paperwork involved. If anything you go Thailand and check out yourself for real. If all else fails tell your lady to jump in a boat and do what other people do she will get a house fone and free money from the UK government bcoz doing it legit doesn't work.
Or wait until two days before your extension runs out and do a minivan border run leaves early morning and your back late afternoon same day costs 3600 baht