What law did she violate? Is a question that no one wants to answer.
Contempt of court.
Whether or not she was morally right or wrong in refusing to issue marriage licenses, once she received a court order to desist, she (or the county) should have secured legal representation to fight the contempt charge.
By continuing to show up for work and refusing to do her job, she stuck her thumb in the eye of the court, and as a result of the contempt charge, got her ass stuck in jail.