In 1914, Maffett graduated from the University of Texas Medical Branch.[1] She undertook an internship at the New York Infirmary for Women and Children, and subsequently she established an abdominal surgery practice in Dallas, in 1915.[1] In the same year, she opened the health center at Southern Methodist University, only resigning as director in 1949.[1]
Between 1926 and 1943, Maffett was associate professor of gynecology and obstetrics at Baylor University College of Medicine.[1] When this moved from Dallas to Houston in 1943, she became professor of clinical gynecology at the Southwestern Medical Foundation in Dallas (now part of the University of Texas Southwestern Medical Center).[1] Maffett worked across several Dallas-area hospitals, including Baylor, Parkland, and Medical Arts.[1] She also completed postgraduate work at the University of Chicago, further training in urology at Johns Hopkins University, and studies in New York.[1]
Maffett was the first president of the Texas Federation of Business and Professional Women's Clubs (1919–20), and later as president of its national affiliate (1939–44).[1][4] She was active in a number of medical associations, including the American Medical Association, Southern Medical Association, Texas Medical Association, American Medical Women's Association, and the American College of Surgeons.[1] In 1944, Maffett attended a White House conference on “How Women May Share in Post-War Policy-Making,” focused on encouraging more women to take an active role in positions of responsibility.[2]
During World War II, Maffett was part of the National Civilian Advisory Committee to the War Department, and chaired the subcommittee that studied health and recreation in the Women's Army Corps.[1] She was a member of the Chinese Relief Region and on the board of directors of the American Bureau for Medical Aid to China, leading the national Federation of Business and Professional Women's Clubs to assist Chinese nurses in 1941.[1] A financial-aid program for the improvement of educational opportunities and facilities for Chinese nurses supported nurses in China through 1949, and nurses in Taiwan after 1950.[1] Maffett was awarded the Rosette of the Order of the Brilliant Star, noted as being instrumental in enlisting the support of thousands of American women for China's first Army Nursing School.[5]
In 1964, a residence for nurses' and students' was constructed at the National Defense Medical Center in Taipei, Taiwan.[1] The Federation of Business and Professional Women's Clubs had raised more than $100,000 for the project, and the building was named for Maffett.[1]