Investigators say they believe Whitfield shot Turner, her father, and two others Wednesday night in the 7400 block of South Stewart.
Whitfield has been charged as an adult with first degree murder and three counts of aggravated battery with a firearm.
Another defendant, 19-year-old Gerald Lauderdale, faces lesser charges in connection with the same shooting.
Mayor Daley spoke about the murder of Chastity Turner before an anti-violence march Saturday along 500 E. 61st in Chicago's Woodlawn neighborhood.
Daley said Chicagoans should be outraged over the death of another child. He said police have taken steps to keep children safe this summer.
But he said parents need to do more. He called on them to keep track of where their children are and what they're doing