Adacia Chambers, 25, was arrested after the crash on a driving while under the influence charge, and authorities said yesterday they added four charges of second-degree murder.
Police did not immediately respond to messages seeking a more detailed explanation of the new charges.
But Chambers' attorney Tony Coleman 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."
"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.
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"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 were killed and at least 46 others hurt, including at least four critically injured. Hospitals initially said five were critically injured but one of those was upgraded to fair condition yesterday.