Don't be fooled, after she get the green card maybe she still make the divorce difficult. If the marriage is really doesn't bona fide, he could divorce her without her sign it. I have a friend did so, kind the same case. Some states has law that if a
marriage couple don't live together for the period of time, it will be considered as separate that can lead to a divorce. Just contact a divorce lawyer to get more advice, and say if in the court she doesn't want to divorce, he can proof that she does it in a purpose, but he should have the evidence, I believe the law will be in his side.