Investigators say evidence suggests Olivia Carolee Culbreath, 21, of Fontana was intoxicated when she drove at speeds of more than 100 mph Sunday and crashed her car head-on into a sport utility vehicle on state Freeway 60 in Diamond Bar, the Los Angeles Times reported.
Culbreath's passengers -- her sister, Maya, 24, and a friend, Kristin Melissa Young, 21 -- were killed.
All four occupants of the SUV -- Gregorio Mejia-Martinez, 47; Leticia Ibarra, 42; Jessica Jasmine Mejia, 20; and Ester Delgado, 80, were also killed.
Olivia Culbreath and Joel Cortez, who was driving a third vehicle involved in the crash -- survived.
Olivia Culbreath was hospitalized at LA County-USC Medical Center jail ward, where she was held on $6 million bail.
Los Angeles County District Attorney's Office spokeswoman Sarah Ardalani said no charges had yet been filed relating to driving under the influence.