The boy, who cannot be named as he was aged 17 at the time of the offences, fatally stabbed Emma Lovell in the heart after he broke into her family's house north of Brisbane about 11.30pm on Boxing Day in 2022.
Following a successful appeal on Friday, the teen will now serve a minimum of about eight years and four months in detention instead of about nine years and nine months before he is released under supervision.
Victims of youth crime ambassador Lyndy Atkinson, who had worked with the Lovells since before the original sentencing, said the family now felt additional trauma.
"They are a broken family ... (the teen defendant) will be able to get out and live his best life," she said.
"Lee Lovell has lost a wife, his two girls have lost a mother. To me, it is still on the side of the offender and victims are continually being left behind."
Queensland Attorney-General Deb Frecklington said the appeal was an unacceptable outcome and claimed it was caused by the previous Labor government's "weak laws".
"I am now looking at my options to make an appeal to the High Court," she said.
Queensland opposition leader Steven Miles said he did not want to "score cheap political points" but was shocked by the decision and thinking of the family.
Mrs Lovell's husband Lee, who was wounded during the home invasion, was unable to attend court on Friday when the appeal decision was handed down.
The home invasion led to "adult crime, adult time"' changes in Queensland law that allow for youth offenders to face a mandatory life sentence for murder with a minimum 20 years before parole.
"The murder of Emma Lovell rocked the state and Queenslanders made it very clear enough is enough and change needed to occur," Ms Frecklington said.
"The community and Emma's family will be devastated by this outcome and our thoughts are with them on another very difficult day they should never have had to endure."
Justice Tom Sullivan in May 2024 sentenced the teen, then aged 19, to a maximum of 14 years with a requirement to serve 70 per cent of that time in detention, after he found the crime to be "particularly heinous".
The Court of Appeal on Friday allowed the teen's appeal against the length of his sentence, with two of the three judges agreeing it was "manifestly excessive".
In his dissenting opinion, Justice John Bond stated he was "respectfully" not able to find the sentence unjust or plainly unreasonable.
Justice David Boddice found the 14-year sentence should stand but reduced the detention period to 60 per cent.
He cited the teen's guilty plea, "genuine remorse and prospects of rehabilitation" as special circumstances justifying his release from detention after serving less than the statutory 70 per cent.
The teen had appealed Justice Sullivan's "particularly heinous" finding in a bid to get his overall sentence reduced to 10 years.
However, Justice Boddice found Justice Sullivan's decision to impose the maximum overall sentence available at the time was correct as the offences were "properly described as provoking a sense of outrage".
The teen now has five years left to serve in detention after 500 days of pre-sentence custody in May 2024 were recognised as time served.
The teen's male co-offender, also a juvenile, was acquitted of murder at a judge-only trial in October.
He was found guilty of burglary and assaulting Mr Lovell, and in December he was sentenced to 18 months' detention - time he has served.
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