Beatriz Jimenez told the Orange County Register she was waiting at a red light when Eloisa Madrigal was crossing the street Saturday with her two daughters.
"They had taken about 10 steps when the car plowed through a red light," Jimenez said. "The girls and their mother were flown into the air."
The driver of the car never attempted to stop, so Jimenez tore off after her, cutting her car off and trapping her until police arrived.
"I got out of my car and I asked her, 'Do you know what you did?' And she shook her head," Jimenez said. "She showed no pain or guilt…it looked like she didn't care."
Jessicah Louise Cowan faces felony charges of murder, driving under the influence of alcohol and causing bodily injury, driving with a blood-alcohol level over 0.2 percent and possession of marijuana while driving.
Cowan faces 15 years to life if she is convicted, and was being held in lieu of a $1 million bail.
Madrigal was in a coma after suffering head trauma. Her daughter Grecia Meza, 6, also suffered head trauma, but is expected to survive. Her other daughter, Osmara, was killed.
Jorge Omar Meza said his daughter Osmara's death "tore me to pieces" and called Jimenez "a hero."
"I just didn't want the driver to get away without paying for what she did," Jimenez said.