Mills served as a board member for the Fresno High area for the last 17 years, Superintendent Bob Nelson said in a statement.
Nelson said Mills advocated to increase students' access to arts, athletics and programs, including the district's International Baccalaureate and Career Technical Education programs.
Since being diagnosed with Lou Gehrig's disease, Nelson said Mills continued to serve the district and advocated for the rights of people with disabilities.
"We stand in her debt, and she will be missed. We will release any additional details as they become available, but at this point, our interests lie with sending love and condolences to Carol's family and friends in their time of grief." Nelson wrote.
Mills' family released the following statement through Fresno Unified:
"We're heartbroken at the loss of Carol. She spent her life in service to others and will be deeply missed. We ask for the respect of our privacy as we mourn our loss."