He also pleaded guilty to driving with excess breath alcohol.
Williams' only child, Byron Williams McLean, read an emotional victim statement to the court.
His voice quavered as he said he'd lost not only his mother, but someone he had accepted as a stepfather.
"My mother was a solo parent, who sacrificed and did everything she could for me as her son.
"She was an amazing mother, and I'm fortunate to have had her as a parent.
"When I first learned of my mother's death, from a policeman outside my work, I cried for many days and nights from grief."
McLean had since married, and said he'd had to consciously ignore his mother's absence, so that he could try to enjoy his wedding day.
He said he'd tried to be strong and resilient, as otherwise he worried it would destroy him.
"I can vividly recall my mother lying in state in Wellington Hospital's morgue.
"A cold, bruised, and damaged empty shell of the warm, loving, and vibrant woman she was.
"It hurts me still to know that she died in such a horrific way, and I do a pretty good job of trying not to think about it most of the time.
Williams' mother struggled through tears to tell the court about the devastating impact losing her daughter had.
Shirley Williams, 87, said she missed the daily calls and twice weekly visits from her daughter.
"She would normally bring a white iceberg rose from her garden when she visited.
"I have very much missed her calls and hearing her voice. I miss her calling out 'Mum', as she alighted from the car.
"She was a ball of energy, and in spite of everything, loved everybody and had empathy for others.
"Whilst I have had a lot of support from friends and family, nothing can fill the gap that Delia has left."
Crown lawyer Kate Feltham said Williams had followed Stevens out of a house, trying to stop him driving because he'd been drinking.
While Stevens claimed he'd been trying to leave a volatile situation, Feltham said there were other options open to him.
Williams fell to the ground during the altercation, and was trying to get back up when she was run over.
Feltham said Stevens had made no attempt to stop and check if Williams was injured.
She added that while Stevens said he hadn't realised he hit her, that was hard to believe as both the front and rear wheels of the car went over her at slow speed.
Defence lawyer Judith Ablett-Kerr QC said Williams had grabbed the door of the car, which flew open, before Williams "disappeared".
"His intentions were good, he wanted to leave what he saw as an escalating situation, and get away.
"But of course, once she disappeared, he should not have continued his manoeuvre without finding out what had happened to her."
In sentencing, Justice Simon France said he accepted the death was an accident, but added that it was an accident caused by gross carelessness.
Police had previously been called to 10 domestic incidents between Williams and Stevens.
Stevens had six previous drink driving convictions.
