The Court of Appeal has reserved its decision on an attempt by Sandy Graham to overturn her conviction for the murder of Dale Watene, who was killed in 2020 and later found buried in Longwood Forest near Ōtautau.

Graham was in the Christchurch courtroom on Monday for the hearing, which was heard by a three-judge panel of Justices Mallon, Fitzgerald and Isac, NZ Herald reported. After a full day of evidence and legal argument, the judges said they would give their decision at a later date.

Watene was killed on 16 April 2020 at Ōtautau in western Southland. His body was discovered about a month later, on 18 May, buried in the forest. Police said he had died from a shotgun blast to the mouth.

A jury in the High Court at Invercargill found Graham guilty of murder in June 2022 after a three-week trial. Justice Gerald Nation sentenced her in November 2022 to life imprisonment and ordered that she serve at least 13 years before being eligible for parole, describing the killing and cover-up as "callous and merciless".

The trial heard Graham lied about Watene's disappearance, pointed suspicion at other people and recruited her friend George Hyde to help bury the body. Hyde was convicted as an accessory to manslaughter for helping after the killing and received eight months' home detention.

At trial Graham said the shooting was an accident and that she could not remember who pulled the trigger. She said she hid what had happened because she feared Oranga Tamariki would take her children.

Her appeal argues the trial was unfair because her experience of domestic violence was minimised and the case was affected by misconceptions about how abused women behave. She also says her trial lawyer, Philip Shamy KC, gave ineffective assistance by not calling witnesses or presenting evidence about violence from Watene and earlier partners, her alcoholism, and police safety orders and 111 calls that she says would have backed her account. She contends the psychological report put before the jury was not thorough enough.

Her appeal lawyer, Elizabeth Hall, told the court Shamy's defence "fell well below the standard" expected and undermined Graham's narrative.

Crown lawyer Stuart Baker rejected that, saying the appeal continued the lies Graham told after the shooting. He said Shamy had done nothing inappropriate and Graham had every opportunity to give her account at trial. He described her version of Watene's death as "a story".

Giving evidence, Graham accepted she had lied in the period immediately after Watene's death, saying she did so out of fear for herself and her children, but maintained she told the truth at trial. She described physical, financial and psychological abuse by Watene.

Professor Denise Wilson, an expert on family violence, told the court she believed Graham's account, saying it matched the pattern she had heard from more than 200 women in her research, and that abused women often tell disjointed stories and share only what feels safe.

Shamy agreed family violence had shaped much of Graham's life but said concentrating on her relationship with Watene had been a tactical decision made on her instructions, and that expert evidence on domestic violence "wouldn't have added anything". He said he might have worded some questions differently.

Graham's appeal against both conviction and sentence was lodged in January 2023. The Court of Appeal has not indicated when its judgment will be released.