Willebrandt was born Mabel Elizabeth Walker in
Woodsdale, Kansas, on May 23, 1889. Her father, David W. Walker, edited a local newspaper. In February 1910, she married Arthur Willebrandt, the principal of the school where she was teaching, and they moved to
Phoenix, where he recuperated from tuberculosis while she finished college and supported them on a teacher's salary. She graduated from Tempe Normal School, later
Arizona State University, in 1911. In 1912, the Willebrandts moved to
Los Angeles, where she taught elementary school and attended night classes at the law school of the
University of Southern California. She received her
law degree from the University of Southern California in 1916 and an
LL.M. a year later. During her time at USC, she was a member of
Phi Delta Delta legal sorority. The Willebrandts separated in 1916 and divorced in 1924. Her efforts led courts to permit the testimony of both men and women. She also campaigned successfully for the enactment of a revised
community property statute at the state level. After graduating, she opened a practice in downtown Los Angeles with Fred Horowitz, who later built the
Chateau Marmont. During
World War I, Willebrandt served as head of the Legal Advisory Board for
conscription cases in Los Angeles. In 1921, at age 32, her law school professor and mentor Frank Doherty, as well as Senator
Hiram Johnson and all the judges in southern California, recommended her for the post of
Assistant Attorney General in the
Warren G. Harding administration. ==Prohibition==