She and a victim inside the truck were both killed in a fiery crash along the Silver Strand in Coronado at the end of the high-speed chase on Thursday.
At least six vehicles were impacted.
Sheriff's investigators said the woman approached two people who were detailing the truck in Imperial Beach and threatened them with the knife. She took the car while a man was still in the backseat.
The identities of the victim and the carjacker were not released.