I've been married to my wife for 3 years who is a non us citizen. She received her green card the beginning of this year and I instantly noticed she changed for the worse. We do not get along anymore and I am currently seeking a divorce. It seems she was only in it for the benefit of green card. We've been separated since May 2011 and I've moved on but is there anything I can do to throw a wrench in her plans of US Citizenship.

Report the "fraud" (if that is what you believe it is) to INS. They may or may not be interested.

Of course, they'll also take a closer look at you to see if you were a participant in a fraud. You have nothing to worry about if that is not the case.