Jara Lee Dix, 21, pleaded guilty in the County Court on Thursday to kidnapping and intentionally causing injury, after her co-offenders Harley James Dix, 28, and Benjamin Keith Judge, 29, entered guilty pleas to the same charges earlier this year.

Jara Dix and Harley Dix plotted to kidnap and assault the 19-year-old victim over the way he treated a family member.

On the evening of March 15, Jara Dix and Judge picked up Judge's younger brother, Steven, and the victim and drove to the One Tree Hill lookout on the pretence of having a smoke.

But once there, the Judge brothers set upon the victim - most of the assault committed by Benjamin - while Jara Dix yelled, "You shouldn't have f***ed with the family".

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The victim thought he was hit in the head with a sledgehammer, and police later found blood on it belonging to him.

During the assault the victim began to lose consciousness and thought he could die.

He grabbed a kitchen knife from his pocket and jabbed at Steven Judge, hitting him in the arm and chest area, before fleeing.

Steven, aged 24, died from his injuries at the scene.

Jara Dix's defence counsel Timothy Sullivan told the court his client was "sad and troubled" from a young age, experienced the death of her father five years ago, and had suffered mental illness.

Psychiatrist Dr Lester Walton gave evidence that Dix's depressive illness had some contribution to her offending, but she did not feel remorse for the victim when he spoke to her.

Mr Sullivan said his client had expressed remorse to him, committed no prior or subsequent offences, and entered her pleas early.

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He said her infant son was a "protective force" and her prospects of rehabilitation were very good.

An immediate term of imprisonment was warranted, Mr Sullivan said, but a shorter than usual non-parole period was appropriate.

"She has the ability to make a productive life for her and her son," he said.

Lawyers for Harley Dix and Benjamin Judge made further submissions, following the return of reports.

Dix's lawyer Markorius Habib submitted his client could not be considered to stand on the same footing as his co-offenders.

He said Dix was not aware of and did not intend for weapons to be used, and he was entitled to a discount in his sentence for his admissions to his involvement in the plan.

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Mr Habib also said Dix had intellectual disabilities and a traumatic childhood.

Dix had avoided further offending while on bail, Mr Habib said, and continued to engage with services.

He said a community-based order would be more effective and meet the needs of community protection than imprisonment, where Dix could fall under criminal influences.

Judge's defence counsel Sarah Wallace said her client had assisted police from their arrival at the scene, giving them details of what occurred and who was involved.

She said Judge had no prior offences and in the lead-up to the kidnapping and assault, had experienced the break-down of his relationship and related stresses.

She also submitted Judge pleaded guilty at an early stage, was at risk of harm in custody due to his small stature and appearance, and had experienced some delay.

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Ms Wallace said the death of Judge's brother amounted to extra-curial punishment.

These factors, she submitted, meant the judge could find reason to not impose the mandatory custodial sentence for kidnapping.

But Crown prosecutor David Cordy said the matter was too serious for a community corrections order or even an order in combination with a jail sentence, saying the maximum 12 months' imprisonment available for a combination sentence would be "an inadequate response".

Mr Cordy said the intention of the kidnapping was to tie the victim up in the bush for days.

"They planned it, they thought about it, they had plenty of time to give it up and walk away, but they didn't and it all turned very bad," he said.

The three co-offenders were taken into custody at the conclusion of Wednesday's hearing.

Judge Patricia Riddell said she would seek a further report on Jara Dix and adjourned the matters to December 2 for sentencing.

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