There are so many cases and stories of how people in Cambodia were able to come here to the US (not talking about during the refugee immigration period).
One of the reason why people choose the marriage or fake marriage is because it speeds up the process. The person in the US goes to the government and ask them to assist in the paper work to send it over to the Cambodian officials. With this, Cambodia government can't really reject. One of the benefits of becoming a US citizen is sponsoring your immediate family or spouses overseas so they have to grant that.
I have a friend in Cambodia who have tried for so many years now to come to the states but unsuccessful. Like your cousin he is highly education and speaks, read and write English fluently, heck I think speaks perfect sentence than me LOL. Even though he works with Foreigners from different countries and can afford his own living and such he still can't come. The Government in Cambodia make it extremely hard for those who wants to come to the US or out of that country for even just a short visit. Why? One of the reason is because they fear that their people will not return. (Stupid i think. If home is a good and safe place to be, who would want to not return? You think this will make them think about reorganizing? I haven't seen that happend yet). Anyhow, so in order to be able to leave the country for a visit (not doing the fake or real marriage) the person must have put lots of collateral. This is why you mostly see the weathly ones get to come visit the US often and very easy. They know that those people have assets back in Cambodia that they must return to claim or take care. Otherwise, it will get turn over to the government. My friend had the money to come and start a living in the states but he doesn't not have any assets to use as an insurance to go back.
Someone suggested the student Visa, it is an option but again might be difficult without the asset stuff. (Sound like our Government is a god digger?) Anyhow, if she ever gets to the states and allow only a period of time to stay, then the pressure is on. The clock start ticking probably as soon as she know that she can leave Cambodia to sort of get to know someone in the potential of getting marry. Because this is probably the only way she can stay in the states permanently.
Basically either way you look at it - marriage whether real or fake, might just be the only reason why she is able to stay in the states. I might be wrong but according to the various stories I've heard.
If you were to go get consultation from lawyer, I would think that an American rep would be best since they know what is expected or what both countries are seeking. Also, might able to avoid mixing Business with Pleasure like with some Khmer reps I've heard.