Dietz had extensive injuries and was in "very critical" condition when she was taken to Mission Hospital trauma facility.
"After several hours of surgery, she did not survive," Rahaeuser said.
The driver initially told police he thought the victim had intentionally walked in front of his truck, but police have ruled out suicide as a cause of the accident.
"For unknown reasons, she [Dietz] entered the roadway," Rahaeuser said.
The driver, a San Clemente resident, was ruled not responsible for the accident after police determined he was sober and driving under the 40 mph speed limit.
Alcoholic beverage violators cited
Four men were cited on suspicion of furnishing alcohol to minors during a Feb. 17 "Shoulder Tap" decoy operation by the Laguna Beach Police Department.
The decoys, 18 and 19 years old, asked persons to purchase alcohol for them at various stores throughout the city by tapping them on the shoulder.
Several adults declined to buy alcohol for the decoys, but four persons were detained, cited and released for furnishing an alcoholic beverage to a minor, a misdemeanor.
Those cited for furnishing alcohol to a minor were: Allan Sterling, 35, of San Clemente; Donald Sutton, 22, of Laguna Beach; Ronald McHenry, 56, of Laguna Beach; and Jacob William, 23, of Laguna Beach.
In addition, three others were cited after being observed by detectives allegedly furnishing alcohol to minors. They are: Corey Sparkuhl, 24, of Laguna Beach, an employee at Gina's Pizza, 1100 So. Coast Highway; Matthew Benusa, 20, of Laguna Beach; and Daniel Contreras, Jr., 24, of San Marcos.
Two minors were also cited for consumption of alcohol in violation of the law: Jaime Takajo, 20, of Escondido; and a 17-year-old whose name was not released by police.
Personnel costs associated with the "Shoulder Tap" program are refundable by a grant the Laguna Beach Police Department has received from the Alcoholic Beverage Control.