In what is believed to be the first case prosecuted under new child abuse laws, a Palmerston North mother who knew her daughter was being raped by her partner but did nothing has been sent to prison.

In the Palmerston North District Court yesterday Judith Noeline Annette Burnett, 34, became the first person sentenced since a 2012 government law change brought in to punish those who stay silent about child abuse.

The law was introduced following public outrage at the deaths of Auckland babies Chris and Cru Kahui, and their family's refusal to cooperate with police investigating the murders.

In an unusual move, Judge Barbara Morris refused Burnett name suppression because the child wanted her mother's name published.

Judge Morris said the mother of four's sentence of two years and one month in jail, for failure to protect a child from the risk of sexual assault, was both a "denunciation and a deterrence".

"The courts must give a clear message to the community that parents who expose their kids to a risk of sexual abuse can expect a sentence that matches society's utter condemnation of this conduct.

"Prison is the only sentence that can offer that."

In 2006, Burnett met the man who would rape her daughter, and moved in with him.

She found out soon after that he had been previously convicted of sexual assault and attempted rape.

Child, Youth and Family were concerned about the man's access to Burnett's daughter and made them both sign a safety plan saying the daughter would never be alone with him.

In 2009, when Burnett was in hospital, her daughter told her that Burnett's partner had been making her touch him inappropriately. Instead of telling anyone, Burnett sent her home with him alone.

The girl began to become unsettled around the house and one night Burnett heard the girl ask Burnett's partner if he wanted a sex act performed on him.

His response when Burnett questioned him about it was: "I've been [having sex with] her for a while now."

Later that night police came round to the house looking for Burnett's partner, but she did not tell them about his admission.

At a doctor's visit soon after, Burnett was asked specifically if she had any concerns about someone sexually abusing her daughter, to which she said no.

She continued to leave her children alone with him.

Crown prosector Erin FitzHerbert said the defendant could at any time have made a simple phone call saying what she knew, but chose not to.

As a result of the man's offending, the girl had reverted to the behavioural traits of a 5-year-old, Ms FitzHerbert said.

Burnett's lawyer, Mike Ryan, said no offending could have been committed by Ms Burnett before March 19, 2012, because there was no law in effect.

The daughter was removed from Burnett's care on October 5, 2012, leaving an offending period of six months.

Mr Ryan said the sentencing also needed to take into account the fact that Burnett did not cause her daughter physical harm.

"You can't divide up the harm between the [offending of her partner] and this offending.

"This may be the first case of its kind. There will be other cases when general deterrence will demand a prison sentence but this is not one of those cases."

Judge Morris said the morality of Burnett in not stopping the sexual assault before the law change was important background for the sentencing.

Her lack of disclosure had made the offending by her partner more possible, Judge Morris said.

The offending by her partner would also have had greater impact because she could not go to her mother for support or to get away.

"I would suggest that would have a devastating effect on a child, and it did."

Judge Morris reduced the sentence, which carries a maximum of 10 years jail, to a starting point of four years.

That was reduced again to two years and one month, because Burnett had no previous convictions, she had pleaded guilty and had shown signs of remorse.

She had broken up with the offender and taken her three other children away from him.

Burnett wiped a tear from her eye as she left the dock.