STILLWATER, Okla. — A woman faces second-degree murder charges after authorities said she plowed a car into the crowd at the 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 announced Sunday she was being held on four additional counts of second-degree murder.

Stillwater police did not elaborate on the reasoning behind 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.

Chambers’ attorney Tony Coleman said at a press conference that 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 and did not appear to be someone who had been in a “drunken stupor.” 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.

“She doesn’t remember a whole lot about what happened. There was a period where I think … she could have even blacked out,” Coleman said. Chambers only recalls people removing her from the car and being extremely confused, he said.

Witnesses described a scene of chaos as bodies flew into the air from the impact and landed on the road. Three adults and a 2-year-old boy, who wasn’t immediately identified, were killed and at least 46 others were hurt, including at least four critically injured. Hospitals initially said five were critically injured, but one of those was upgraded to fair condition.

The dead adults were identified as Nakita Prabhakar Nakal, 23, an MBA student from India at the University of Central Oklahoma in Edmond, and a married couple, Bonnie Jean Stone and Marvin Lyle Stone, both 65, of Stillwater. Marvin Stone was a retired professor of agricultural engineering, who had been popular with students, a colleague said.

“He was loved by students and one of the best teachers we had,” said Ron Elliott, the former head of the Biosystems and Agricultural Engineering Department at OSU. “He just really had a gift for connecting with students and helping them learn,” Elliott said in a telephone interview.

Among the injured were nine children 10 years old or younger.

At the corner of the intersection where the suspect’s car came to a stop, a makeshift memorial continued to grow Sunday with balloons, flowers, stuffed teddy bears and candles with black and orange ribbons tied around them, for the school’s colors. A handmade sign read, “It’s always darkest before dawn. Stay strong.”

Anthea Lewis had tears in her eyes as she placed a child’s hat with an Oklahoma State University logo at the base of the memorial.

One of the injured had been a baby sitter for Lewis, she said.

“I’ve lived here my whole life and this blows my mind,” she said. “This is something that doesn’t happen in Stillwater.”