Each state's laws are different. The best way to find out what might happen is to make an appointment with several divorce lawyers. They usually offer the first half hour free. This is her chance to see if the lawer will work for her and to get some questions answered.
No, it will not affect any court proceedings. "Adultery" is not a crime, and is not recognized as such in the United States of America. The spouse may bring it up during court hearings to show character, but the court can not and will not base their decisions on whether or not someone has cheated.