Hi, Thank you everyone for your responses.
I just wanted to expand on my question and answer some of yours. My wife has a US and Thai passport. But a US citizen must use the US passport for the whole trip from the USA. A US citizen cannot enter or leave the USA on a foreign passport. Also, they must use the US passport for the whole trip by US law. US immigration will look for the stamps from the other countries on the trip. So she must travel on her US passport to Thailand and back. I did confirm this with the US passport office.
Right now she has a 90 day O visa but she plans to stay 118 days. So, if I understand right. Before the 90 days is up she can cross the border at Chom Chong into Cambodia and for a fee get the Cambodia entry stamp and then cross right back into Thailand and she will have another 60 days as a tourist in Thailand. Does this all sound right?
Someone mentioned getting an extension to her O visa at a local immigration office. Is that actually doable with an O visa? From what I think I understand on the Thailand Embassy Washington DC website (which could be more informative, but it's not), that may not be the case. Anyone know of someone getting an extension at the Burrium Immigration office to an O visa?
FYI, when we sent in for the O Visa we did not know that Thailand had changed the entry from 30 days to 60 days with a possible 30 day extension.
Thank you, BOB