She needs to get out of this fast with the help of an immigration and possibly a criminal al defense attorney so that she doesn't get prosecuted. Get an attorney before filing a complaint with ICE.
She does need to hire an immigration attorney first think in the morning.
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I strongly suggest that your GF notify the UsCIS that her spouse married her in order to obtain a green card and that the marriage is a sham. She does not want to be charged with marriage fraud which is a federal crine and can mean a fine and/or prison time.
All she has to so it not show up for the interview. I suggest she file for a divorce.
It sounds as though your girl friend is a U.S. citizen. In that case, the case can probably be resolved though either withdrawal of any petition she has filed or though divorce. She should consult with an experienced immigration attorney for assistance.
While this answer is provided by a Florida Bar Certified Expert in Immigration and Nationality Law, it is for general information purposes only and an attorney/client relationship is neither intended nor created. You should seek out qualified counsel to review your case and provide you with advice specific to your situation. Call +1-561-478-5353 to schedule a consultation with Mr. Devore.
Contact and set up an appointment with an immigration attorney as soon as possible. I strongly recommend you do not discuss this further in an open forum such as this