A woman who plotted with her lover to murder her husband, is appealing her sentence on the basis of being a domestic abuse victim.

Amandeep Kaur, 33, and Gurjinder Singh, 28, were found guilty in 2016 of the murder of Kaur's husband, 35-year-old Davender Singh.

Singh's throat was slit as he sat in his car on a south Auckland road on August 7, 2014.

His neck was so deeply severed that a pathologist said it was classified as a "partial decapitation".

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Kaur and Gurjinder Singh were each sentenced to a minimum of 17 years behind bars.

Today in the Court of Appeal, her lawyer Ron Mansfield said the sentence was "manifestly excessive".

He said there was an element of self-defence in the murder, as Kaur had been trapped in a loveless, controlling and abusive marriage.

He said Kaur's husband had put a voice recorder on her without her knowledge, to check up on her relationship with Gurjinder. Her husband would also ring her several times throughout each day.

Mansfield said that while there was no police record of abuse being reported, there was a clear pattern of abusive behaviour.

"There can be a reluctance to disclose or report, as the victim blames themselves or normalises it.

"The complexities of a different culture, especially for women who are not on equal footing. Given that there was evidence already in the notes, of violence, at least from 11 July, the appellant should have been assessed by health professionals."

Mansfield then read from one of the notes Kaur sent to her lover, which had been translated from Punjabi to English.

"Please love save me from him, please, please. I do not want to die being with him.

"Please do not tell anything with your wife, please, otherwise he will beat me again."

However Crown lawyer Simon Barr said there was no evidence of domestic abuse, and pointed to a pattern of vengeful behaviour from Kaur.

Barr questioned Kaur through a Punjabi interpreter, about a letter she wrote from prison where she said Gurjinder's family needed to lose 10 people, because her husband had been equal to 10 people.

She answered "Yes I wrote that, but I was in prison at the time and was in shock. I wasn't myself."

Barr said Kaur had told Gurjinder's wife that he needed to "admit" to the murder.

He then referenced conversations Kaur had had with her brother, where she had given him the address of Gurjinder's family in India, and suggested her brother should harm them.

Barr asked if it was true she had written a letter suggesting her brother kidnap Gurjinder's four-year-old son from the village, and only release him if she told him it was okay.

Kaur answered that she couldn't account for everything she did when she first went to prison, as she was very angry and wasn't herself.

"At the time I was in a mood to take revenge.

"I am sorry for that.

"His son is mentioned there, and my brother is mentioned there. I have mentioned a son in there but the kidnapping is of Gurjinder's brother.

"When I wrote that letter I felt helpless, and nobody was helping me at that time.

"At that time my brother and sister-in-law asked me for that address and I gave them that address, and I admit it."

Barr then turned to another incident, asking Kaur if she had tried to have a work friend fired in the past, because she thought they were going to tell her husband about her affair.

Kaur said she might have talked about it, but she never made an official complaint about her work friend.

The Court of Appeal has reserved its decision.

When Kaur and Gurjinder Singh were sentenced last year, Justice Graham Lang imposed a higher non-parole period because of the seriousness of the crime.

He cited the deliberate planning over several weeks, and 13 knife wounds to the victim.

He said that the pair was equally responsible, as while Gurjinder Singh carried out the physical aspects, he believed Kaur was the instigator of the offending.

The pair's infidelity had been discovered by Gurjinder's wife, who then informed Kaur's husband, Davender Singh.

Three weeks later Davender bled to death in his Honda Torneo on Norman Spencer Dr.

Police found handwritten notes between Kaur and Gurjinder, plotting the attack.

On the night of the murder, Gurjinder Singh followed Kaur and her husband after work and struck when they pulled over to talk.

In sentencing, Justice Lang said the evidence pointed to Gurjinder Singh cutting the victim's throat while Kaur held her husband in his seat.