STILLWATER, Okla. — A woman faces second-degree murder charges after authorities said she plowed a car into the crowd at an Oklahoma State University homecoming parade, killing four people, including a toddler.

Adacia Chambers, a 25-year-old resident of the college town, was arrested after the Saturday crash on a driving while under the influence charge, and Stillwater police said Sunday she was being held on four additional counts of second-degree murder.

Police did not elaborate on the new charges in a statement announcing them, and a spokesman did not return repeated messages seeking comment. Officials with the Payne County district attorney’s office couldn’t immediately be reached.

Tony Coleman, Chambers’ attorney, said his client may suffer from a mental illness. He also said she did not smell of alcohol when he met her hours after the crash. Police are awaiting blood tests to determine if she was impaired by drugs or alcohol.

“I absolutely can rule out alcohol,” Coleman told a press conference in Oklahoma City, adding that he had spoken to her aunt, grandmother and boyfriend and all had said she was not drinking. He added it was his opinion that she suffers from a mental illness and said there were warning signs from her behavior before the crash, including an inability to sleep.