Judge Weir said Hulton-Donnelly had previously been dealt with in the Youth Court on 15 matters, including a charge of robbery. She also had been dealt with in the Rotorua District Court for 23 different offences, including nine convictions for violence.
"You are only 18. What are we going to do with you?" Judge Weir asked.
The judge said the pre-sentence report was bleak and said while Hulton-Donnelly had been on remand in custody she had been seen behaving inappropriately and had been unco-operative.
Hulton-Donnelly's lawyer, Max Simpkins, said his client was the oldest of eight children and had left school at 12. She had taken on the mother role and would babysit the other children while her mother went out and socialised.
Mr Simpkins said Hulton-Donnelly had no father and a mother who was "hopeless". Hulton-Donnelly would be in the same prison as her mother, who was an alcoholic.
Judge Weir said he was sympathetic to Hulton-Donnelly's background. He said the starting point was four years' jail and reduced the sentence to give her credit for her guilty plea and to take account of her lawyer's submissions.
Another woman, 21-year-old Zarnia Te Arongimara Renata-Curtis, of Tauranga, was due to be sentenced in the Rotorua District Court on Friday but Judge Weir adjourned sentencing to see if a suitable address could be found for Renata-Curtis to serve home detention. She will now be sentenced on June 22.
The 12-year-old was referred to Rotorua Police Youth Aid. Two others are expected to stand trial for their part.