A 14-year-old girl was in police custody after she allegedly hit her mother in the head with a hammer or other blunt object, officials said.

The girl was arrested Sunday following the attack in the family's Scripps Ranch home about 15 miles north of downtown San Diego.

The 56-year-old mother was not expected to survive, homicide Lt. Kevin Rooney said.

The woman's husband and 21-year-old daughter were sleeping in the house when they were awakened by a loud scream. Police were called around 9 a.m. and found the mother in the kitchen with serious head injuries.

Rooney said the girl, whose name was not released because she is a juvenile, was arrested on suspicion of assault. Police are investigating the motive for the attack, and the relationship between the mother and daughter.

Neighbors told the San Diego Union Tribune the victim was Becky D'Aoust and said she had a 14-year-old daughter.

Neighbors said the family is quiet and close.

"I can't believe it," neighbor and family friend Mary Cederlund, 86, told the newspaper.