In the notable feminine side of the Stinson family, younger sister, Marjorie, learned to fly and attended the Wright School of Aviation in Dayton, earning her license on August 12, 1914, the ninth U.S. woman to do so and the youngest at age 18. Like her sister, she became an air mail carrier.

In 1915 Katherine and Marjorie instructed in their own Aviation School in San Antonio with their brothers, Eddie and Jack, as mechanics. There they trained Canadian cadets for the war, who became known as the "Texas Escadrille," and Marjorie was called the "flying schoolmarm." The girls also flew many exhibitions for the Liberty Loan Drive.

The Stinson School closed in 1917. Marjorie, after their school closed, barnstormed fairs and air meets until 1928, giving up flying in 1930 to work as a draftsman for the War Department. When she died in 1975 at age 79, her ashes were symbolically scattered over Stinson Field in Texas from a 1931 Curtiss Pusher. (K O Eckland)