Moko Rangitoheriri's killer argues she was driven to violence by the little boy's bad behaviour, and so she shouldn't have to spend so long in prison.

Tania Shailer was sentenced to 17 years in prison at Rotorua High Court on June 26 for killing and torturing Moko while he was placed in her care. But her lawyer has appealed, saying the sentence was "manifestly excessive".

Tania Shailer and David Haerewaare appealing their 17-year prison sentences for the manslaughter of Moko Rangitoheriri. Photo: George Heard/FAIRFAX NZ.

Her partner David Haerewa, who received the same prison term from Justice Sarah Katz, is also expected to appeal his sentence.

When the sentence was read out last month, there was a collective sigh of relief from Moko's family sitting in court. Many had been reduced to tears in the public gallery. Whanau were held tightly. Others just held their heads in their hands when the brutal manner of Moko's death was read out.

Moko Rangitoheriri was tortured and killed by Tania Shailer and David Haerewa.

Now, the revelation that Shailer is arguing for a shorter sentence – essentially on the grounds her three-year-old victim was badly behaved – has outraged her family.

The use of the provocation defence in court was abolished in 2009 after Clayton Weatherston used it as an excuse for murdering girlfriend Sophie Elliot.

In Shailer's case, her lawyer Ron Mansfield made a written submission to the court that the stress placed on his client had driven her to the crime and it was a mitigating factor when it came to her sentencing.

Arama Ngapo-Lipscombe, lawyer for Moko's mother, says Nicola Dally-Paki was upset by the grounds for appeal.

"My client is absolutely devastated that the woman who killed her baby would put the family, including the children of Shailer and Haerewa, through another painstaking event.

"My client is disgusted at any suggestion that one of the grounds of appeal may suggest that baby Moko contributed to the torture he received in Shailer and Haerewa's care. The blame for their horrendous actions fall at their feet. They alone are responsible. They are despicable people. Nicola describes them as evil and this just supports her view that they deserve a life sentence."

Moko suffered vile abuse at the hands of caregiver Tania Shailer and her boyfriend David Haerewa. Supplied.

The injuries inflicted on Moko were so severe it shocked New Zealand. When he was finally brought to Taupo Hospital by paramedics after weeks of abuse he had facial and neck contusions and abrasions; human bite marks on the left cheek, right cheek and arms; lacerations to his chin, neck, ears and lip; haemorrhages to both eyes; and multiple abrasions and contusions over the skin of his chest and abdomen. His bowel was also ruptured, causing infections, making him very weak.

His head was so swollen he was unable to open his eyes. The pathologist had trouble determining the exact cause of death.

Shailer says three-year-old Moko had hit her own children.

"Rather than appropriately manage Moko's behaviour towards her children, her attempts to curb or punish his behaviour became violent," her defence lawyer Ron Mansfield argued.

"This tragic transition is detailed to assist the Court to correctly determine the defendant's culpability and not to seek to blame Moko."

Mansfield is quick to not take away from the tragic loss of life at his client's hands at sentencing.

"My duty in court is to talk to culpability and help people understand what's happened in this case to ensure it doesn't happen again," he says.

"And to ensure we impose a sentence the fits the culpability of the offending and actions for which they have plead guilty to."

Crown prosecutor Amanda Gordon had pushed for life imprisonment saying the extent of offending was in the most serious of categories.

However Justice Katz says it is appropriate to impose a finite sentence and placed a final term of 17 years in prison. This appeared to be received well by some of Moko's family.

Mansfield has labelled the term of imprisonment excessive.

"It was too high given her personal mitigating factors and when compared with other sentences imposed in similar cases," he says.

He listed Shailer's guilty plea, her mental health and the fact she had no previous conditions as mitigating factors that should have lessened Shailer's sentence.

"Her conduct has arisen as a result of her previously being a victim of significant violence, her mental health, the personal and financial stress the family was under, the poor behaviour traits of Moko and his sister as a result of their own exposure to violence, and her attempts to self-medicate."

"Her violent acts were the direct result of her mental health condition and her inability to cope with the added pressure and stress placed upon her. The defendant took no satisfaction from the harm inflicted upon Moko."

A report by Dr David Chadlow, an experienced forensic psychologist, concluded Shailer was labouring under a mental illness at the time of offending. She was also thought to be suffering from post traumatic stress disorder as she was also the victim of domestic abuse.

"The defendant's ability to control her response to the children and or appreciate the harm she was inflicting on Moko was severely diminished," Mansfield says, quoting the report.

"In regard to Moko she failed to remember that he was a three-year- old boy that was acting out dramas he himself had experienced (including violence to other children).

"It was apparent to me her stress triggered rage and rage triggered violence."

Mansfield argued the most serious cases of abuse occurred when Shailer was "out of it on a cocktail of drugs".

Her drug use, combined with her mental illness complicated her mental state further and this should be considered a mitigating factor.

A start date of 14 years for Shailer was his recommendation. He also requested a discount of 17 months for mitigating factors to the crime as well as a 25 per cent reduction for her early guilty plea.

A further five per cent reduction was requested from Shailer's "genuine remorse".

"Accordingly an end sentence of no more than nine years imprisonment is appropriate with a minimum period of imprisonment of no more than four years and six months," Mansfield says.

Minutes after the trial ended Sensible Sentencing Trust founder Garth McVicar predicted an appeal would be lodged based on the sentence length.

Their legal team had predicted a much lesser figure when looking at other precedents. While they were pleased a hard line was taken by Justice Katz in sentencing, they were realistic in their expectations.

"It reinforces what we have been saying – the laws need to change. It puts pressure on Chris Finlayson to change the law," he says.

McVicar says Shailer's appeal this week would have a perverse effect on victims.

"It will drive them down into an even deeper dark hole," he says.

"They lose faith in the justice system. We will be encouraging the Court of Appeal to exercise their powers and increase the sentence imposed on Shailer.”