quite possibly, no issues her. But the O visa and retirement extension will cost her in and around 40,000 baht.. ..15 months total......thereafter, 14 to 16,000 yearly for renewal. Jus' saying. .... Peace of mind for sure and seamless.
Google and official Thai websites explaining the matter clearly are a great invention. First you do your initial research and the hard work and then you come to a forum to clear up any unclear details. That's how it works
unfortunately there has been a lot of abuse on the Visa exempt entries with lots of people trying to work on them. Therefore a few genuine tourists, as you may be, end up paying for them. Thailand is focused on short-term mass tourism, 10 to two weeks, a quick cash grab. Your thinking is correct and will give you peace of mind.