Michelle Lowry, 51, was driving a 2001 Hyundai Excel east on Highway 128 just east of Wragg Canyon Road when the crash happened around 4:40 p.m., CHP Officer Jaret Paulson said.
Lowry's car swerved toward the right side of the road, Paulson said. She overcorrected and the car swerved to the left then went down an embankment and struck a tree.
Lowry was not wearing a seat belt and was ejected from the Hyundai, Paulson said. She was taken by helicopter to Queen of the Valley Medical Center in Napa where she was pronounced dead.
The CHP is investigating whether alcohol was a factor in the crash, Paulson said.