"I veered to the left, and then I saw her hit the center divider. Then, I hit the center divider and my air bags just deployed," Nicolas said.
Prosecutors allege that Nicolas had no idea traffic had stopped in front of her and that she was distracted when she slammed into the back of 23-year-old Deanna Mauer's car, ultimately killing her.
One expert testified Nicolas was driving nearly 90 mph at the time.
"I don't agree that I hit the rear of the Hyundai, but I agree that we made impact," Nicolas said.
Jack Jeffries, who was also involved in the accident, contradicted her account. Prosecutors played a recorded telephone interview Jeffries gave an investigator saying he believed Nicolas's Prius crashed into Mauer's Hyundai.
"It was like a bomb. I thought there was an explosion. I looked in my mirror and saw the girl hit me on the side," Jeffries said.
If Nicolas is convicted, she could face a maximum of 6 years in prison.
Closing arguments are set to begin at 9 a.m. Wednesday.