Get whatever visa she can get. My sister in law and mother in law both got 10 year multi visit visas first time out. My wife to be got extensions on her 6 month visa by buying the proper extensions in time from immigration.....
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 ).