It ruled that a life sentence was not appropriate because Wihongi's mental impairment was a big factor in the offending.
The three Appeal Court judges said that, overall, "we see this as a case of a battered defendant who has reacted in an extreme way to her abuser".
Wihongi is one of only three murderers in New Zealand who has not been given a life term.
Under the Sentencing Act, life imprisonment is compulsory on a murder conviction, with finite penalties available only if a judge determines that a life term would be manifestly unjust.
The victim was the father of five of Wihongi's six children and the couple, who were living apart at the time of the murder, had a long history of violence to each other. She had previously blinded him in one eye by throwing a bottle at him.
At trial more than 500 pages of police reports on domestic incidents between the pair were produced.
After an initially happy upbringing, Wihongi changed dramatically aged 13 after overdosing on pain killers following a family argument.
The immediate pathological consequences were that she could not speak or walk properly. Behavioural problems followed and she dropped out of school. Her life then became one of "victimhood," the courts were told.
Wihongi turned to alcohol and was sexually abused at age 14 by a drug and alcohol counsellor.
Soon after, she was in a sexual relationship with her future partner's older brother, who prostituted her for drugs and money.
Through him she met the murder victim and the couple were in a tempestuous 17-year relationship, both drinking heavily.
There was also gang involvement, and she was gang-raped. Subjected to a home invasion, she was assaulted with a full bottle of beer in front of her children and was scarred around the neck.
Experts gave evidence of Wihongi displaying complex features of post-traumatic stress disorder, and anxiety and depression. She also abused alcohol.
Before the murder, Wihongi and her ex-partner had been drinking with another man before starting to argue and shout. Their daughter, aged 11 at the time, watched her father walk out of the house and her mother get a knife from the kitchen and follow him.
Wihongi lunged at him on the path outside, stabbing him hard in the chest.
The bleeding victim and his daughter got into Wihongi's car which was in the driveway and took off. Wihongi followed with the other man in his car.
Not far away they came across the first vehicle which had crashed into a fence. The driver was slumped over the steering wheel semi-conscious, and neighbours with medical training were trying to help him. One said Wihongi came up to the car and was punching the victim through the window. She was later arrested for a breach of the peace at the accident scene and taken to the police station.
Meanwhile, the 11-year-old daughter picked up the knife used by her mother to stab her father, took it inside and washed the blood off it. She then took her younger siblings to a friend's home nearby and rang their grandmother to come and get them.
