She offered no further details in her statement.
Stewart had been at the helm for only six weeks. He was also the first Black director of the agency.
Republican state lawmakers on Wednesday said Stewart was asked to resign. State Sen. Jake Hoffman said in a statement that Stewart had made "questionable moves on consulting contracts" and had received a reprimand while working at the agency in 2020.
Arizona Gov. Katie Hobbs' second pick for head of Arizona's child welfare agency was asked to resign due to "questionable moves on consulting contracts."
Republicans accused Hobbs of not thoroughly vetting nominees.
This all comes on the heels of the governor withdrawing her nomination earlier this month of Dr. Theresa Cullen to lead the state Department of Health Services.
A Republican-led state Senate committee considering Cullen’s nomination raised concerns about pandemic business closures and curfews in Pima County, where Cullen serves as the public health director. So, Cullen opted not to proceed with the nomination.
She remains Pima County public health director.
Hobbs said she suspected politics was at play among Senate Republicans.