An advocate on Tuesday said the boy's appeal was an insult to Vyleen White's traumatised family and there would be community outrage if the original sentence was not upheld.
The boy was 16-years-old when he fatally stabbed Ms White during a carjacking outside a shopping centre west of Brisbane in February 2024.
The crime was the catalyst for controversial "adult crime, adult time" laws, ensuring juveniles face at least 20 years in custody for murder.
However, they were not retroactive and the boy was sentenced under the state's previous laws, receiving a 16-year jail term.
The teen, who cannot be named for legal reasons, pleaded guilty to murder and was sentenced in November 2025.
He is likely to be released from custody in late 2033, about the time of his 26th birthday, after 60 per cent of his sentence with time already served.
The boy appealed, claiming 16 years was excessive for a non-premeditated murder.
Arguments against the teen's sentence were an insult, Victims 1st ambassador Lyndy Atkinson said outside court.
"A precedent needed to be set and this was the right precedent to be set," she said.
Ms Atkinson said the White family were devastated by the appeal.
"They are too traumatised to attend. I think it's an insult to the family and there will be community outrage if the original sentence is not upheld." she said.
The sentencing judge had made an error, defence barrister Matthew Hynes told the Court of Appeal justices on Tuesday.
"This is a case where there is a single stab with fleeting attention," Mr Hynes said.
The teen was serving the highest sentence handed down in Queensland for a 16-year-old who killed someone via a single stab wound, the justices heard.
Justice David Boddice said a brief moment of intent to kill or cause life-threatening injury that turns fatal was enough for murder.
"That's the offence, that's how you get to murder: one moment," Justice Boddice said.
The teen quickly approached the 70-year-old grandmother and demanded her car keys before inflicting a "non survivable" 17cm deep knife wound, Chief Justice Helen Bowskill said at sentencing.
He did not hesitate before stabbing the grandmother as she held up her hands and backed away.
The boy stole Ms White's 2009 Hyundai Getz hatchback and drove it to a nearby residential area where he showed it off to other teens.
CCTV footage had captured the teen deliberately stabbing Ms White as she tried to get away, Director of Public Prosecutions Todd Fuller told the justices on Tuesday.
"The sentence falls well short of being described as being manifestly excessive," he said.
Justice Bowskill's sentence was made in the context of community demands for greater protection from violent young criminals and increased knife crime in public.
"It was accepted that this was murder was particularly heinous," Mr Fuller said.
The three justices reserved their decision.
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