Three people guilty of attacking a teenage woman who was later found unconcious and nearly dead in the Dome Valley have each been sentenced to more than 12 years' jail.

Julie-Ann Torrance and Nicola Jones were in March convicted of the attack during a High Court at Auckland trial.

They laughed and egged on co-accused Wayne Blackett as he unsuccessfully tried to snap the then 19-year-old woman's neck in May 2016.

Blackett next hit the woman repeatedly in the head with a hammer before she was left for dead on a roadside north of Auckland. He pleaded guilty at the start of the trial.

On Friday in the High Court at Auckland, Justice Christian Whata sentenced Torrance to 16 years and seven months in prison and Jones to 13 years and one month jail.

Blackett was sentenced to 12 years and seven months in prison.

Each must serve at least half their full prison terms before being considered for release.

Jones and Torrance's sentences include time to be served for assaulting, robbing and kidnapping the young woman in two separate attacks.

Torrance is also guilty of sexually violating the teen.

While Justice Whata considered Jones had no prior history of violence and showed prospects of reform, he considered Torrance had shown little remorse or acknowledgement of her role in the attacks.

During the trial, the court heard the attacks started after Jones became angry with the young woman early last year because she believed the woman had slept with her partner.

Then in April 2016, the young woman was lured to a former friend's Newmarket flat under the false pretence of a drug deal.

There Jones and Torrance ambushed, bashed and tasered the woman before threatening to repeat the attack if she did not leave Auckland for good.

One month later, Jones and Torrance, along with two others already sentenced to prison terms - Michelle Blom and Jaclyn Keates - kidnapped the woman from near Karangahape Road and took her to Blom's west Auckland home.

There she was bashed with a cricket wicket and bat and sexually violated.

After being held captive for about 22 hours, Jones, Torrance and Blackett drove to Conical Peak Road with the young woman tied, wrapped in a tarp and thrown into the back of a Hilux ute.

After trying to strangle the woman, Blackett took a hammer and delivered at least 10 blows to the woman's head, causing multiple fractures and depressing her brain by 2cm, prosecutors said.

Keates pleaded guilty to her part in the May assault and was last December sentenced to three years' and two months in jail.

Blom was sentenced to more than two years' jail for her role in the attack.