The mother of Dunedin toddler Iris Kathleen Davidson has been sentenced to jail for what Justice Lester Chisholm described as her "unforgivable" neglect of the little girl, who died of brain injuries in October 2002.

In the High Court at Dunedin yesterday, Brooke Lee Small, 27, and a former flatmate, Warihi Tauhore Wharehinga, 42, were both jailed for 18 months, Small for wilfully neglecting Iris and Wharehinga for endangering the child's life by failing to supply her with medical care.

Both were granted leave to apply for home detention.

Wharehinga's partner, 23-year-old Rebecca Jane Lunt, was sentenced to 100 hours' community work and 12 months' supervision, with conditions relating to assessment, counselling and treatment for drug and alcohol use, and any treatment identified from psychological or other assessments.

Iris died of non-accidental brain injuries on October 19, a day after her emergency airlift from Aramoana to Dunedin Hospital, and little more than two weeks before her second birthday.

The fatal injury was inflicted during the 24 hours before her admission to hospital.

Medical examinations revealed numerous fractures and healing injuries to her arms and legs, an injury to her pancreas, mouth injuries and 29 separate bruises, as well as a seven- to 10-day-old head injury that made her brain vulnerable to the second and fatal injury.

The timing of the injuries indicated an escalating pattern of violence, Justice Chisholm said.

Although allegations were made about who caused the injuries, the jury had not been able to determine responsibility, and neither would he.

But the fact that Iris was being injured, if not the precise nature of the injuries, must have been apparent to anyone living in the same house.

The injuries would have caused Iris "considerable pain and suffering", the judge told Small, Wharehinga and Lunt.

All three were living in the Heyward Point Rd house with Iris and Wharehinga's child from about March 2002 until Iris' death. Small had become depressed and Wharehinga invited her to stay with them.

He and Lunt effectively looked after the child for at least the first two months, until Wharehinga told Small to assume more responsibility for Iris' care.

Justice Chisholm said that from the extensive medical evidence at the trial, it was clear Iris was subjected to violence from about early September.

He told Small her unforgivable neglect of Iris called for a sentence to deter her and other parents of very young children.

He said Wharehinga was entitled to credit for the efforts he and Lunt made to help Iris and Small, and for pleading guilty to endangering Iris by failing to get medical help.

He agreed that Lunt's responsibility was less than either Small's or Wharehinga's.