Everything depends on the facts and circumstances of your situation. You really need to take all of your paper work, from both marriages and all immigration applications to an immigration attorney in your area.
Could you please give more information? Did anyone come to talk to you from immigrations or is it something you got in the mail? How are they acussing her of this? What were the circumstances of her first marriage, please give us as much info as you know so we can advise you better. Are you a US citizen?
However my best advice for now is NOT to talk to anyone about this without an attorney present. Please provide more information, so we can help.
