Jessica Barrymore, who, like the actress, was the daughter of actor John Barrymore, would have turned 48 on Thursday.
"Although I only met her briefly, I wish her and her loved ones as much peace as possible," Drew Barrymore told ABC News in a statement. "I'm so incredibly sorry for their loss."
According to the San Diego County Medical Examiner's Office, Jessica Barrymore was found in her car and shortly thereafter, the fire department confirmed that she was dead.
A cause of death has not yet been determined.