A two-year-old "happy, fearless explorer" was going on a big adventure with her grandmother when a five-second lapse in attention caused it to go "so horribly wrong", an Adelaide court has heard.

The 64-year-old woman, who cannot be identified for legal reasons, was taking her two granddaughters to Waikerie in July 2020 when she hit a broken-down truck on the Sturt Highway at Shea-Oak Log, north-east of Gawler, killing the two-year-old and injuring the six-year-old.

The grandmother also sustained serious injuries in the crash and had to be airlifted to the Royal Adelaide Hospital.

The District Court heard the much-loved grandmother had handed out lolly snakes to her grandchildren and was changing a song through her mobile phone when she took her eyes off the highway for up to five seconds, smashing into the side of the truck.

In sentencing on a charge of death by dangerous driving, Judge Liesl Chapman said the grandmother was devastated by the consequences of her actions, and that she had not been speeding, was well-rested and not under the influence of drugs or alcohol.

Judge Chapman suspended the woman's sentence of one year and six months.

"No good at all would come from you being jailed for what happened, it would only compound the tragedy if that is possible," Judge Chapman said.

"This is a tragic reminder to us all of the dangers of up to just five seconds of inattention on the road."

Little girl's death left 'gaping void' in family

The toddler's parents told the court through a victim impact statement there had been a gaping void in their family since their daughter's death.

"Although she was the youngest and smallest of us all, her big personality somehow seemed to take up a lot of space," director of public prosecutions Martin Hinton read on her parents' behalf.

"She was a happy, fearless explorer, constantly on the lookout for new and interesting experiences.

"We miss her terribly every single day."

The court heard the woman had relocated from interstate some years ago to be an ongoing presence in her grandchildren's lives and that the "the hard-working, sweet grandmother had devoted her whole life to her close family".

"Mum is still very much a loved member of our family — although she has through a momentary lapse of judgement made a terrible mistake — we still care deeply about her," the victim's parents wrote.

"The girls loved their grandmother and she loved them; it was an incredibly special relationship.

"They were all looking forward to going on a big adventure together that went horribly wrong."

Grandmother admits fault 'totally'

The woman's lawyer, Michael Woods, told the court that his client accepted that it was "totally and utterly her fault".

"She loved her two granddaughters and the last thing she wanted to do was put them in danger," he said.

"No-one should have to bury their child … it's so very different knowing you're the one that's caused that grief and that makes that very difficult indeed.

"She thought [the death of her husband of 31 years] would be the worst thing that happened to her, until July 15, 2020."

The court heard the 64-year-old had apologised privately to her family and wanted to apologise to all the people who attended the crash scene and helped.

The woman had no prior criminal convictions, an "impeccable" driving record and had never had an accident prior to this one.

The grandmother has entered into a one-year good behaviour bond and has been disqualified from driving for 10 years.