Los Angeles - A teenage girl has been arrested after killing her sleeping mother by pounding her head with a hammer, according to the San Diego Tribune on Tuesday. Police said they had no motive for the crime, which occurred while the victim's husband and other daughter were asleep in the house. The family awoke to screams and called police, who arrested the 14-year-old perpetrator. Medics found the victim with severe head injuries, and she died later in hospital. The victim was named as Rebecca D'Aoust, 56, a counselor at an elementary school. The incident occurred in the prosperous Scripps Ranch community just outside San Diego.