Fisher joined the District in 1959, when she was hired as an English teacher at Northside High School, later renamed Marshall High School. She served as the district's first Dean of Girls and then as head counselor at Marshall during the 1960s.
The Air Force transferred her husband to England for two years, and when the Fisher family returned to San Antonio in 1971, Mary Lou was hired as a counselor at Holmes High School and her husband, Potts, was hired as a counselor at Marshall. Potts died suddenly in 1972, and at the request of teachers, administrators, and the superintendent, Mary Lou was asked to return to Marshall to replace her husband.
In 1974, Fisher was appointed head counselor at Marshall, a position she held until she retired in 2002. She says the best part of her job was getting the opportunity to help so many young people, and through the years, many former students have contacted her to thank her for her support.
Her impact on students went far beyond Marshall High School. As a member of the Northside Guidance Steering Committee in the 1980s, she developed a guidance curriculum for the District that was later adopted by the state and implemented in all Texas public schools. Fisher also brought recognition to Northside during her stint as editor of Guidelines, the Texas Personnel and Guidance Association monthly publication.
Throughout her career, she received numerous awards from military and civilian organizations, and she also was a recipient of the Rhosine Fleming Award for Outstanding Counselor of the Year from the South Texas Personnel and Guidance Association. In addition, she and her family, which includes two children and five grandchildren, established the Mary Lou Fisher Scholarship, awarded annually to low-income Marshall graduate who plans to attend junior college.
Fisher passed away in September 2015.