How obtain a permanent resident visa for my friend?

Question

I would like lawers answers please.
I have a friend (man,american nationality) who is married whith french woman since 8 years (they get married in the USA).
They have 2 childrens, both have french and american passports and one of the two was born in the USA.
Few month after their marriage, they decided to come back to France to live.
After seven years of living in France, the last year, they went back to live to the USA.
But the spouse can't obtain the permanent resident visa, and green card neither.
And, in July, the woman and her 2 kids came to France for Holidays and when they came back to the United-States, they were bloked by the customs and they could not enter in the us territory.

And my question is how can she do to obtain her visa to join her husband in USA?
I don't understand why a woman married with an american since 8 ans with 2 americans kids couldn't live with her family in the United-states?
Thank you by advance to give me an answer asap

Answer 1

As your friend found out, being married to an American doesn't automatically grant permission to live in the US. (By the way, that's true of all countries in the world.)

The American husband must petition for his wife; she must apply for an immigrant visa and then a green card.

Answer 2

It's a long process, my friends wife has been trying for 3 years, she's from Canada.

Answer 3

Have you ask the custom n immigration dept....