She has to apply at the embassy in thailand and show money in the bank, family ties there, a job, something to bring her back to Thailand. If the paperwork is filled out correctly, ! she should get a visa. My wife got one for 6 months and we got married in the states. (everything goes on hold now). There are permits you can buy (of course) to extend her stay. Now, her mother and sister applied first time and both got 10 year, multi visit visas first time around. (They visited once ).
I changed my flight with QA and they only had Econ+ available, so I paid 1800 usd extra for the seats and then got a bill on cc for 400$ change fee......