it's not about getting a job, it's about getting an ED visa. Most Muay Thai fighters make peanuts too and knowing Thai isn't a career option, but one can get ED visas for those.
well, people can get one for Muay Thai or self defense... If they provide it for those, I wouldn't be surprised if they provide one to become a dive master.
With the current rules, at no point in time, BUT, Thai immigration could decide at anytime that an overstay could affect her chances of getting a visa in the future. Furthermore, an overstay here could affect her immigration status in other countries.
Go visit your local immigration office and ask these questions. As for your 12 month visa, the only option is an ED visa. A semi work around would be to return to the UK, get a 6-month multi entry tourist visa that you can stretch to 9 months, after which you could try to get a regular 60-day visa from Penang or Cambodia, which is extendable to 90.
That's certainly not the norm. Of course, there are exceptions, and I was in that category, as my now ex-wife was wealthy (through inheritance), but she definitively stuck out in the community as the "richer than her husband" woman. In the VAST majority of cases, Thai wives come from poor backgrounds and seldomly work at all. That said, a "good income" in Thailand is a pittance of maybe 15 or 20K. In fact, marrying a foreigner is akin to escaping poverty.