From experience.... She's going to be denied. As soon as they hear/see boyfriend, fiance, husband is from u.s....they automatically deny it, even before she gets there for the interview. You have only 3 options. K1 finance visa, which is about a 10-16 month wait right now. A spouse visa which is over 2 year wait right now...OR find someone from the UK or some other country, not Thai or u.s., to have a fake relationship with, then when she applies she can say she's going with her UK boyfriend to visit sites and parks ECT. Unless she has a legit business in Thailand that she pays taxes on, or works for that would be willing to say they're sending her for business purposes, she has zero chance of getting a tourist visa right now. The way it was told to us before was, they stop illegal immigrants where they have control. Meaning the ones trying to do it with visas. They automatically assume she's coming and planning to get married while on tourist visa, and stay. No matter how untrue it may be. We travelled to many other countries together, ones she needed visas for, some she didn't. Gave every reason why neither of us has plans to stay in America at all. Detailed plans of the trip. Plenty of money in the bank and possessions and property she owns in Thailand. All the supporting documents PLUS many more. Interview day, she waited about an hour for her interview, they asked 3 questions, and gave her a PRE-PRINTED denial notice. Her interview literally lasted less than 1 minute.
Simple answer....I just don't want to do it myself. Pay for conveniences. Same reason I eat at restaurants. I can do it myself, but I'd rather not that day.
I once rented a condo that I had no clue had a damn tennis court or something above the room. Tried to get money back, and tried to dispute with card company. Never got a dime back. Due diligence is on you