The appeal was heard in the High Court at Auckland last month.

The High Court has upheld a judge's decision to discount an offender's jail sentence by a third because of her Māori cultural background and deprivation, despite opposition from the Solicitor-General.

The discount was given to Rachael Heta by Judge Soana Moala after she pleaded guilty to two charges of causing grievous bodily harm and one of common assault earlier this year.

Heta had stabbed her partner four times in his chest and armpit as he lay in bed. His lung was punctured and spent a fortnight in hospital.

Judge Moala set a start point of six years and three eight months jail.

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She gave Heta a 30 per cent discount for personal circumstances included in a 'Section 27' cultural report that covered Heta's background - that was on top of a 10 per cent discount for participating in a restorative justice process and a 25 per cent discount for her early guilty plea.

The end result was a jail term of three years and two months.

The Solicitor-General appealed the sentence, arguing that while a 30 per cent may be warranted "because of the need to recognise Māori post-colonial experience" and to meet Parliament's intention underlying the principle of cultural reports, the discount of 30 per cent was too high.

The appeal was heard by Justice Christian Whata at the High Court in Auckland late last month.

Lawyer for the Solicitor-General, Mark Lillico cited case law that stated "cultural norms cannot excuse [violence] for some groups but not for others," and said any discount based on the cultural report must be in line with those given in other cases.

"An increased award to recognise the position of Māori is precluded by current Court of Appeal authority," he said, adding that the highest discount available for social deprivation was "in the order of 10 per cent".

In a decision released on Wednesday, Justice Whata traversed the cultural report, completed by Khylee Quince, a barrister and solicitor of the High Court and a senior lecturer in law.

He said Heta was a mother of four. Her background was characterised by alcohol abuse, parental absenteeism and violence. Her schooling was intermittent, she was sickness beneficiary with no qualifications, had been a heavy drinker from age 10 and her personal relationships had been violent leaving her with several prominent scars.

The judge noted the disproportionate number of Māori imprisoned and said the effects of colonisation were well-documented.

He said there was "no express requirement to have regard to systemic Māori deprivation in sentencing", and the case law cited by Lillico contained nothing to suggest the court "was laying down a general rule about discounts for personal background factors".

Justice Whata said there was nothing to suggest discounts for matters contained in a cultural report had to be capped at 20 per cent, and it was up to the sentencing judge to consider the factors of each case.

He noted that Heta's victim had forgiven her during a restorative justice process.

He found Judge Moala had not erred and that the sentence was not manifestly inadequate. The appeal was dismissed.