Casey Mallia was just 19 years old when the car she was travelling in, driven by her boyfriend, crashed on the Sturt Highway at Galore, west of Wagga, on December 22, 2018.

Matthew Luke Agius was driving the car along a two-lane, multidirectional stretch of road with a 100km/h speed limit at the time of the crash.

A Sydney court heard Mr Agius decided to overtake another car travelling at the speed limit, reaching 120km/h across broken lines before returning to the left lane where the lines were unbroken.

He overcorrected the vehicle as the tyres hit the dirt by the side of the road, causing the car to turn on a 90-degree angle, hit a waterway on the opposite side of the road, flip and travel at least 100 metres before coming to a stop.

Casey was found unconscious, hanging upside down in the passenger seat.

Mr Agius was found under the car moaning.

After sustaining massive head trauma, shattered teeth, and internal damage to multiple organs, Casey suffered a heart attack when pulled from the vehicle.

She died in hospital the following day, December 23, due to a lack of blood to her brain.

Her organs were donated on Christmas Eve.

Casey's mum Kirsty Greenfield said her life had not been the same since that day.

"I don't remember the days following her death. I was in daze, I was numb," Mrs Greenfield said.

"Christmas is a traumatic period now, because all I can think about is walking back into her hospital room on Christmas Eve and seeing a shell of who she was."

Mr Agius was charged with dangerous driving occasioning death in 2019, and pleaded guilty.

On August 6, he was sentenced to one year and 10 months imprisonment in the Penrith District Court.

However, Judge Ian Bourke is yet to determine if his jail term will be spent in prison or served in the community through an intensive correction order (ICO).

The court heard Mr Agius sustained brain damage in the crash.

Judge Bourke has ordered a sentencing assessment report and asked that it assess Mr Agius' suitability for home detention and provide an update on his suitability for community service.

"To be honest, the sentence is disappointing and to hear he may not even have to do jail time is even worse," Mrs Greenfield said.

"He decided to speed, he decided to overtake, and his decisions led to the death of my daughter.

"Part of me does feel some empathy for his parents knowing they have to watch their son possibly go to prison, but at the same time I think he's still here, he still gets to come home, he still has a future. I won't get that with Casey."

The moment her daughter died, Mrs Greenfield said she felt as though her entire family were given a life sentence.

"The grief will never go away for me, her father, her step parents, brother, sisters and her niece, it will never stop," she said.

"Her brother Tim was so close with Casey. If he was ever in a bad place, she was the one he went to, and she was the only one he'd talk to - now he doesn't have any outlet, he's so lost, and that's so hard for a mother to watch.

"I don't remember what I told the kids about the accident, but I remember the looks on their faces, and I'm supposed to be the their soft place to fall, but on that day I failed them because I was so broken.

"I feel like I fail them everyday now when they don't come to me to support because they don't want to hurt me more."

Mrs Greenfield and Casey's stepfather Paul, her father Patrick Mallia and stepmother Suzy Mallia, her siblings Ashley, Tim, Autumn and Vicki Mallia, and niece Bella Peters, all continue to grieve her loss.

In a victim impact statement, Tim said he "was absolutely broken" that Casey won't see him "at his best in the future".

Her sister Ashley said in her victim impact statement that the day Casey died was "the day [her] family died", and that it felt "as though [her] heart had been torn from [her] chest and was being stomped on"

Patrick Mallia also gave a statement on the loss of his daughter, saying "never in my worst dreams would I think that Casey would never come home again".

Mr Agius returns to court on September 24.