In 1928 Kathryn married a trial attorney, and four years later the couple moved to Maryland.  Her husband's work sparked her interest in law, so she entered the Washington College of Law at American University in Washington, D.C. and she became one of three women to graduate in the class of 1936.  As a new attorney, she went to work for the Legal Aid Bureau and opened a private practice. 

Mrs. DuFour raised two children while finding time to participate actively in her community.  In 1950, she was elected to the Montgomery County Council.  In 1953, Governor Theodore McKeldin appointed her to the Maryland General Assembly, where she served on the House Judiciary Committee.

In 1955, Mrs. DuFour was appointed as a judge to the Maryland Sixth Judicial Circuit Court, serving Frederick and Montgomery Counties.  This made her the first woman circuit court judge in Maryland.  She was elected the following year to a 15-year term.  She hired her own secretary, and paid her salary.  She was the first judge to hire her own bailiff and private investigator.  She was instrumental in getting a new addition to an old courthouse, as well as in persuading the state and county to raise judicial salaries.

Throughout her long career, Mrs. DuFour was called on to decide cases ranging from child support to rape and murder.  When Judge Thomas M. Anderson was appointed to the Court of Special Appeals in 1967, DuFour became the first woman chief judge of the Sixth Judicial Circuit Court of Maryland.  As chief judge, she created the position of court administrator, assigning cases to various members of the bench.  She so dramatically improved court efficiency and decreased the case backlog that she was credited with having brought the court into the twenty-first century.