The office of Governor Doug Ducey accepted her resignation on Saturday, the Arizona Department of Emergency and Military Affairs said in a statement.
Anthony Cox, deputy director of the emergency management division, would take on the role of acting director, the statement said.
In an email accompanying her departure, Smith-Reeve criticized the state's handling of the COVID-19 pandemic, writing that her role at the helm of managing the crisis was clearly "being addressed by the Governor's staff and ADHS ... which means my presence and function is duplicative," the Arizona Republic reported.
To date, the state has 773 cases of COVID-19, with 15 deaths. Testing for the virus is minimal, hospitals have few beds and face serious shortages of protective equipment, and Ducey has held off ordering shelter-in-place for the state.
In the email, Smith-Reeve wrote that directives issued by the governor's office "have been to work completely outside of the State Emergency Response and Recovery Plan that the Governor acknowledged and directed the state enterprise to follow when signing Executive Order 2017-06," she wrote.
"The lack of communication and transparency is degrading the hybrid process that non emergency management trained individuals have put into place," she wrote, the Republic reported.
Ducey's office did not immediately respond to a request for comment.
His chief of staff, Daniel Scarpinato, sent the following response to Phoenix New Times on Saturday about Smith-Reeve's resignation: "Arizona is grateful to have the very steady leadership of [DEMA Director] Major General McGuire leading our emergency operations during this critical time. We won't miss a beat with him and his team at the helm."