@Richard *******
You worry too much. Once your wife has a new Thai passport obtained from her embassy in Washington, DC, she can use both her US passport and her Thai passport.
***book the flight and check-in to the flight to Thailand on her Thai passport
***exit USA on her US passport
*** enter Thailand on her Thai passport
*** book and check-in to a flight from Thailand to the USA on her US passport
*** exit Thailand on her Thai passport
*** enter USA on her US passport