A 16-year-old girl has admitted killing her mother by repeatedly beating her head with a claw hammer in San Diego.

Heather Marie D'Aoust pleaded guilty to second-degree murder Thursday in Superior Court. She faces from 16 years to life in prison when she is sentenced next month.

D'Aoust attacked her mother in her family's kitchen in May 2008. Rebecca D'Aoust was struck at least 15 times and died at a hospital the next day.

An FBI agent testified that the girl's cell phone had a text message about her plans to kill her mother.

Prosecutors say she suffers from substantial psychological problems.