on a 6-month multi entry Tourist Visa, you get 60 days upon each entry within the 6 month visa validity period. You can extend them ONCE for 30 more days, for 1900.- THB on Immigration. If you exit and re-enter on the last day of the visa validity period, you get stamped in for a last time for 60 days, which you also can extend once for 30 more days. A METV will get you almost 9 months admitted stay, if you get your ducks in a row. . . . . . . if you want a visa that gives you 90 days admitted stay upon each entry within a one-year period, you would need to apply in your home country for a "multi entry 365-days Non-Imm-O retirement or family visa". Or for the 365-days multi entry Non-Imm-O/A retirement visa"
in case you got a "single entry 90-days Non-Imm-O retirement visa", you can only change from the visa to the "one year extension of stay" by showing funds of 800.000.- THB in a Thai bank account. If you don't switch from the visa to the "extension" your time will be up within 90 days. As this visa was a "single entry", you can neither extend or repeat it. You need to exit Thailand before the 90 days stay permit is over
check-in to the flight with her Thai passport, exit USA with her U.S. passport. Enter Thailand with her Thai passport. On return, check-in with U.S. passport, exit Immigration with the Thai passport, enter USA with US passport
and should you already got a TR-visa issued, it means that if you try to get a 30 days visa exempt upon entry, the border official will see your TR visa on the monitor and refuse the visa exempt. He will insist that you use the visa
I have never before read or heard, that Immigration allows you to buy a single re-entry permit on a visa exempt or a 60 days tourist visa. They also have problems with selling you a re-entry permit for a 90-days Non-O visa