The Dome Valley victim was smashed in the head at least seven times leaving round holes in her skull, a court has heard.
A pathologist who assessed the teenager's injuries has given evidence during the trial at the High Court at Auckland where five people are on trial. The victim cannot be named for legal reasons.
The Crown says the victim was kidnapped twice in two weeks, tortured, sexually violated then "left for dead" on the side of the road on May 9 last year.
The alleged catalyst was revenge because the 19-year-old was rumoured to have slept with an ex-boyfriend of one of the defendants.
The accused are Michelle Blom, Nicola Jones, Cameron Hakeke, Wayne Blackett and Julie-Ann Torrance, all charged with varying offences.
The defence lawyers say the defendants are innocent of the charges because some have already admitted what roles they played in the attack.
This afternoon the court heard from medical professionals who had treated the victim's severe life-threatening traumatic head injury.
A pathologist at Auckland City Hospital, Simon Stables, was asked to give an opinion on what had happened to her.
The jury was shown a 3D reconstruction of a CT scan of her skull which had holes to the back, front and sides as well as forehead and eye-socket fractures.
Stables said the injuries were consistent with a hammer being used. The woman had been hit at least seven times and some spots had been hit multiple times, he said.
The holes in her skull also matched tears to a balaclava which the Crown said the woman was found wearing.
She also had injuries on her wrists and ankles consistent with cable ties and "train-track bruising" on her buttocks which could have been inflicted by a cricket bat, Stables said.
She was in intensive care for two weeks before moving to a brain injury unit where she still needed feeding through a nasal tube.
'I thought it was rubbish someone dumped'
Kathleen Tolman found the teenager curled up on the side of the road in Dome Valley on her way to work about 6.45am that Monday, she said in her evidence today.
"I didn't know at first what it was because a lot of people dump rubbish and things in that part of the road and I just thought someone might have dumped something.
"But when I flicked my headlights on I saw the person move, the leg moved."
Listen to 'unpleasant' evidence without prejudice
Jones' lawyer, Maria Pecotic, today told the jury her client had already pleaded guilty to three of the eight charges laid against her - the other five she did not do, including the assault with a Taser.
"She did not do these things that the Crown says they did."
And when Jones texted the victim's mother that she would kill her daughter if she ever saw her again, she never intended to follow through with the threat.
Pecotic told the jurors they would hear "unpleasant" and "plain awful" things during the trial but urged the jury of five women and seven men to put aside feelings of sympathy and prejudice.
Their job was to listen to the evidence dispassionately, the lawyer said.
Blom's lawyer, Julie-Anne Kincade, also said her client didn't commit the offences she was accused of.
After picking up the victim from K Rd on May 8, the defendants went to Blom's house on Great North Rd where they allegedly stomped on the victim's hand, cut her hair, stripped her naked and sexually violated her.
But Blom wasn't part of it because she was upstairs, Kincade said.
Blackett's lawyer, Mark Edgar, said his client also was not there when the alleged assaults took place and he had already admitted attempted murder and kidnapping.
Hakeke's lawyer, Graeme Newell, said his client differed from the other defendants "markedly" because he had only been charged in relation to the first kidnapping two weeks earlier.
Hakeke, a sex worker, only invited the victim to his house in Green Bay and then left to see a client while Torrance and Jones allegedly committed the assaults and kidnapping on April 23.
There wasn't any significant planning, he said.
"Did he intend the victim was assaulted with a Taser, assaulted by having her hair cut, be robbed of her vehicle, intentionally assist in any of the crimes alleged against him?
"Did he have any sort of a plan?" Newell asked.
Charges the defendants face
Nicola Monique Jones, 29, of Tauranga:
Attempted murder, sexual violation, injuring with intent, assault with Taser, threatening to kill.
Julie-Ann Torrance, 42, of Henderson:
Attempted murder, sexual violation, assault with a cricket bat, assault with a Taser, assault with scissors, injuring with intent.
Wayne Edward Blackett, 39, of Manurewa:
Sexual violation, assault with a cricket bat, assault with scissors.
Michelle Blom, 30, of Glen Eden:
Kidnapping, sexual violation, assault with a cricket bat, assault with scissors, injuring with intent.
Cameron Te Hau Kareti Hakeke, 34, Green Bay:
Kidnapping, assault with a Taser, assault with scissors, robbing victim of a car, iPad, phone and other items.