Amber Allen died in a horror crash when a car driven by Kylie Allely at more than 100 km/h slammed into another vehicle on the wrong side of the road at Yallourn North, about two hours east of Melbourne, in October 2018.

The 32-year-old was suffering from rebound fatigue after consuming methamphetamine days earlier.

Allely used the drug every second week while her two young children, along with her stepdaughter Amber, went back into the care of her ex-partner Gareth Allen.

Amber died in hospital, while Allely's five-year-old son and three-year-old daughter were seriously injured in the crash.

"My life and soul has been smashed into a million pieces," Amber's grandmother Elizabeth Allen told the Victorian County Court on Friday.

"The anguish of seeing Amber being loaded into an air ambulance still makes me wake up in a cold sweat. It's not just her death I will grieve but all her hopes and dreams.

"She will never go to high school, she will never date, have a first kiss or first job, learn to drive, get married, or have children herself."

Ms Allen's heart still skips a beat whenever she sees a girl's ponytail in a crowd.

"But then desolation hits me, because it's not Amber and it never will be," she said.

"The feeling of hopelessness and emptiness is overwhelming. I can't always remember how to breathe."

Kelly Bounds, her teenage son Ethan Bounds, and his best mate, Brett Lucas, were also seriously injured in the crash while on their way to a skate park in Moe.

Ethan and Brett struggled to finish high school and suffer lingering physical and mental effects, the court was told.

"My parents say I got into a car as one child and I came out another," Mr Lucas said in a statement.

Prosecutor David Cordy said Allely was seen driving erratically in the moments before the crash.

She has pleaded guilty to one count of dangerous driving causing death, two counts of dangerous driving causing serious injury, and one count of conduct endangering persons.

"Her driving was well and truly below the standard required," Mr Cordy said.

Allely's barrister Rishi Nathwani in Friday's pre-sentence hearing said his client had shown significant contrition and remorse.

"No punishment the court imposes upon her will come close to the punishment she will impose upon herself until the day she passes away," Mr Nathwani told the court.

The barrister also read aloud from a statement Allely wrote.

"There are no words to describe how sorry I am to my baby girl Amber," she said.

"I would give anything, including my own life, to have her shining light here again."

Allely, who remains on bail, is expected to face a further plea hearing on December 15.

Australian Associated Press