It took about 20 minutes that morning to recover the bodies of the sisters, ages 7 and 9, from their mother’s fully submerged car, upside-down in the murky Petaluma River. Divers found them still strapped in their seat belts.

The girls’ mother, Alejandra Hernandez-Ruiz, 27, of Rohnert Park, survived the Aug. 31, 2016 crash on Petaluma Boulevard North near Gossage Avenue.

Friday, she was arrested, and now, she’s in the Sonoma County Jail on $500,000 bail, charged with two counts of vehicular manslaughter, felony child endangerment and driving with a suspended license.

Hernandez-Ruiz will appear in court Tuesday to seek a reduction in her bail.

She faces up to 11 years and four months in prison if convicted in the crash that killed sisters Sayra, 7, and Delilah Gonzalez, 9.

It was unclear exactly what triggered her arrest more than a year after the crash. Brian Staebell, a spokesman for the District Attorney’s Office, would not release details, saying only it was “the totality of her conduct while driving” that resulted in criminal charges.

The crash happened just after 8 a.m. Hernandez-Ruiz had dropped off the children’s father — her partner — at his work site and was headed to Rohnert Park to take her daughters to Waldo Rohnert Elementary School.

CHP officers at the time said she was driving in the left lane of the divided four-lane boulevard when her Chevy Impala LS drifted into the median. When Hernandez-Ruiz overcorrected, her car shot back across the roadway and down a steep 20-foot embankment just north of the Petaluma Village Premium Outlets, crashing through heavy brush and oak trees, before overturning and sliding into a narrow stretch of the river that runs along the boulevard.

The car quickly sank in 6 feet of water and was fully submerged.

One driver who witnessed the crash pulled over and scrambled down the embankment, where he saw the mother standing on the car.

Police officers and firefighters arrived within minutes. They dove in to get the girls, still strapped upside down by their seat belts in the water-filled car, but could not free them in time. The girls were pronounced dead at a Petaluma hospital.

In the immediate aftermath, investigators found no evidence of car or booster seats. State law requires car or booster seats for children until age 8 or they reach a height of 4 feet 9 inches. It was unclear whether the younger girl required one.

A CHP spokesman said Hernandez-Ruiz told investigators she had been cut off in traffic.

The crash mirrored one a week earlier in which two sisters were killed after their mother lost control of the family car on a wet road and plunged into the Russian River near Jenner. The crash was investigated and no charges were filed.

You can reach Staff Writer Paul Payne at 707-568-5312 or paul.payne@pressdemocrat.com. On Twitter @ppayne.