Diane Warrick has also been charged with an enhancement for allegedly using a knife to kill 70-year-old Mary Jane Scanlon inside her home in the 1800 block of Elinora Drive in Pleasant Hill on Wednesday afternoon.
Warrick had been hired through a Craigslist ad to care for Scanlon, who was in a wheelchair, police said. She had recently become a live-in caretaker.
Cope said the attack appears to have followed a minor dispute about where she parked her car.
Warrick has a history of mental problems and had previously been committed to Patton State Hospital in Southern California for life, Napa County District Attorney Gary Lieberstein said.
Her commitment stemmed from a 1997 incident in which she shot at four Napa County sheriff's deputies at Napa State Hospital.
She was convicted in 1999 of four counts of attempted murder of a peace officer, three counts of kidnapping, burglary and being a felon in possession of a firearm. But, during the sanity phase of the trial, she was found not guilty by reason of insanity, Lieberstein said.
In 2002, Warrick returned to Napa County for a sanity hearing.
The district attorney's office contested Warrick's request to be declared sane, but a judge found that she had regained sanity and no longer represented a danger to the public, Lieberstein said.
She was released to an outpatient program in Contra Costa County under the supervision of the Contra Costa County Conditional Release Program.
In 2003, she was released to a community treatment program in Contra Costa County, Lieberstein said.
Warrick is scheduled to be arraigned this afternoon in Contra Costa County Superior Court in Martinez.