Hay was superintendent at Pasadena Hospital nurses' training program in California in 1905 and 1906, and chaired the Pasadena branch of the Los Angeles County Nurses' Association. She was a member of the council of the California State Nurses' Association, and an associate editor of the ''Nurses' Journal of the Pacific Coast'', a quarterly publication. She was also head nurse at the Iowa State Hospital for the Insane in her early career. She served as superintendent of the Illinois Training School for Nurses, and as nursing superintendent at
Cook County Hospital, from 1906 to 1912. She went to Europe with the American Red Cross in 1914, leading a group of American nurses with Jane Delano. From 1914 to 1915 she was matron of the American Red Cross hospital in Kiev; she described meeting
Nicholas II of Russia for a Red Cross magazine. She went to Bulgaria to help establish and lead a nurses' training school there, at the invitation of the
Tsaritsa,
Eleonore Reuss of Köstritz. In 1917 she was named Director of the Bureau of Nursing Instruction for the American Red Cross, and she helped to organize the U. S. Army School of Nursing in Washington, D.C. She was assigned as Chief Nurse of the Balkans Commission of the American Red Cross in 1918. In 1919 she was at
Philippopolis supervising war relief work. In 1920 she succeeded
Alice Fitzgerald in Paris as Chief Nurse of the Red Cross Commission in Europe. In 1921, she laid the first stone at the dedication of the American Nurses' Memorial in
Bordeaux, France. She was awarded a Florence Nightingale Medal for her work. She was also awarded the
Gold Cross of St. Anna in Russia, and the Bulgarian Royal Red Cross. ==Later life and legacy==