In general, how difficult is it for an average Thai woman to get a tourist visa to visit the US? Someone who doesn't have any real assets and has a basic education ie. finished high school or even has a college degree. Does the fact that she would be accompanied by her American boyfriend help her case? What exactly does the US embassy here want to see when they decide whether or not to grant a tourist visa to a Thai woman?

The same as for anyone else. That they intend to return to Thailand at the end of their visit and have the funds to provide for themselves. An American boyfriend would not indicate a high probability of her return to Thailand I suspect.

BobChittie: This topic was discussed at great length just a month ago, so please go back through the threads and you will find exhaustive discussion of what is required. Also check the Department of State web page, with particular attention to why people are turned down.

The chance of getting the Thai lady, of which you speak, into the U.S. is very slim, based on the imformation you provided. Accompanying her just makes it harder, as the law required mindset of the consular officer interviewing is her intent is to stay over her visa unless you prove to them otherwise, and you being along suggests that if you stay in your homeland and fail to return to Thailand, she will stay with you.