Olivia Culbreath of Fontana was arrested Sunday on suspicion of driving under the influence and manslaughter after being pulled from a badly mangled Chevy Camaro on State Route 60, CHP Officer Rodrigo Jimenez said.
She remained hospitalized Monday in serious condition with a broken femur and a ruptured bladder, officials said.
Jimenez said the crash scene in Diamond Bar, a suburb east of Los Angeles, was horrific. Three people were ejected from their cars and the Camaro was barely recognizable.
Authorities said Culbreath was traveling north in the southbound lanes of State Route 57 before transitioning east in the westbound lanes of State Route 60, where the Camaro collided head-on with a red Ford Explorer. A Ford Freestyle then collided with the Explorer.
Four people were pronounced dead at the scene, and two people died after being taken to a hospital, Jimenez said.
Five females and one male were killed, said Los Angeles County Coroner's Lt. Larry Dietz. Officials were waiting to release their names because relatives have not been notified.
Witnesses told dispatchers the Camaro was speeding up to 100 mph, Jimenez said.
Jimenez told the San Gabriel Valley Tribune evidence collected from the scene included alcohol.
The victims included a 24-year-old woman from Chino and a 24-year-old woman from Rialto, Los Angeles County coroner's Lt. Fred Corral told the newspaper. Both were passengers in Culbreath's car who died at the scene.
A family member told KCAL-TV one of the victims was Culbreath's sister.
Another victim, a 47-year-old man, is believed to have been a passenger in the Ford Explorer. The driver of the Ford Freestyle suffered minor injuries.
The westbound lanes of State Route 60 were closed for about eight hours as investigators sifted through the wreckage.