When officers approached the vehicle, the driver pulled out a replica handgun and brandished it in a threatening way.
At least one of the officers opened fire and shot the woman.
She was rushed to local hospital where she was pronounced dead, authorities said.
Officers said there was no way of knowing whether the gun real or not.
"In this case, this replica is virtually indistinguishable from a regular firearm. It shares all the same characteristics of a regular-looking deadly gun," said Lt. Dave Dolson from the Los Angeles County Sheriff's Department.
The woman has not yet been identified, and police are still unsure why she brandished a replica handgun at CHP officers.
