Detectives say 33-year-old Amy Waters of Simi Valley tried to help suspected shooter Mark Connole escape police.
Officers say Waters picked up Connole shortly after he opened fire and helped him flee.
After a short chase, officers eventually arrested the two without incident.
Waters has been charged with felony evading.
One person died in the shooting, and three others were hurt.
Police say the shooting began after the victims met Connole at Fallbrook Mall for unknown reasons, where an argument took place, leading to the deadly shooting.
The investigation is still ongoing.