I have been waiting 2 years this month, we’re told to expect appointment for embassy interview in January at soonest, but I have heard of people getting it done in 18 months
I didn't fill out anything I just go to the place across the street from the embassy and give them the copy of marriage license, 2 photos, copy of the house book, and they fill out the forms for you, put together the whole packet for 200 baht no problem takes them less than 15 min. You need to be there early in the morning to apply for the visa, and pick up in the afternoon the next day. I like to go on Tuesday or Wednesday, if you are over 60 they will usually come out and pull you out of line and take you to another window so you don't have to wait so long. I know a Aussie that takes crutches and they get to him right away.
If she lives her a certain amount of time outside the U.S. I believe 330 days in a year you pay no taxes, also you can claim a deduction on any taxes paid to Thailand. So you do not have to give up US citizenship.
Some one else will probably give you better advise. You need to make an appointment. It is a affidavit costs $50 to get stamped I got mine in USA embassy. Thai will need document showing she is not married. Don't forget the Thai department of state paper work.