The L.A. County Sheriff's Department received a call early Wednesday morning reporting someone made threats via Twitter.
The student was identified by 6:30 a.m. and sheriff's detectives arrived at her Lawndale residence and confirmed she had sent the messages. The teen was arrested for felony criminal threats and booked at Los Padrinos Juvenile Hall.
A warrant was served at the residence to search for possible weapons, the sheriff's department said.
Extra deputies were sent to Lawndale High School Wednesday.