Ok. Before the experts start telling you that statements have to be stamped, it's crap! Bangkok Immigration (biggest in the country) accept the emailed statements WITHOUT a stamp. That's a fact. If some pissant provincial office doesn't accept it, elevate it to a higher level.
If you've only been meeting since March I don't hold out much hope for you at this stage unless she has a good job with decent salary for a length of time. The UK government has been stung by Thai girls getting into the country and then staying beyond their visa, so they're very strict these days
It doesn't actually "revert". The marriage visa no longer exists, so you need to start from scratch with an "over 50" visa (O, OA, OX, LTR) if a person is over 50, otherwise they will need to seek out a different visa (ED, B, DTV, Elite)