I have seen this scenario too many times. She either is trying to scam you for money in the future or plans to bring her entire family to the US when she has her green card.
In Jordan this happens all the time. You may just have to back away and allow your son to handle this and fall. Then help him stand up again afterwards.
Sometimes we push too hard and lose our sons. I don't get along with my son's wife and she caused major problems and he like your son will choose the one he loves.
It is illegal in the US to marry under false pretense. If she married illegally to just get a green card, you can report her to the FBI. But then you would lose your son.