Amanda Brumfield, 29, was booked at the Orange County Jail on Wednesday. She faces charges of first-degree murder, aggravated child abuse and aggravated manslaughter of a child.
Court records show she told investigators the infant, who died in her care in October, acted normally and ate bananas after she fell from a playpen and hit her head. But detectives believe Brumfield's story is inconsistent with the girl's injuries.
It was not immediately clear whether Brumfield had an attorney. A telephone message left at the jail was not returned Thursday morning.
Thornton's publicist has said the actor hasn't spoken to Brumfield for a number of years.