Authorities say 28-year-old Monica McCarrick stabbed the girls multiple times before attempting to take her own life and set fire to her apartment. Fire and police officials responding to the Oct. 12 blaze found the bodies of the girls, Tori and Lily Ball.
McCarrick was arraigned on murder charges from her hospital bed at John Muir Medical Center on Friday. The Solano County Public Defender's Office was appointed to represent her.
Investigators have not released a possible motive or the weapon used in the attack. But a neighbor who entered the apartment during the fire has said he saw a bloody sword and a bottle of pills in the hallway.
A court hearing on the case is scheduled for Nov. 17.
