@Bill ************
once the 90 day stamp you wife will get runs down to 30 days or less you two should be able to go to the immigration office that serves the area where you stay here and have your wife apply for a "piggy back" extension of stay for 1900baht <- she will get stamped in for the same amount of time you get when you enter (which will be for a year OR as long as your medical insurance is valid for up to a year)
and
once she gets the extension you can buy a multiple re-entry permit for 3800baht