The San Jose Mercury reports the autopsy results raises the possibility Sarah Botill died from drowning instead of alcohol poisoning as first suspected.
She and another girl had a sleepover with the stepdaughter of former Gilroy councilman Roland Velasco at his home last Friday night.
The girls apparently snuck out, got their hands on vodka and started drinking when they returned.
The next morning, Velasco's wife found Botill passed out in the shower with one of the girls trying to sober her up.
Experts say it is possible for someone to drown in very shallow water after they lose consciousness.