Susan Blyth Neill-Fraser, 57, is appealing against her conviction and sentence for murdering her partner of 18 years, radiation physicist Bob Chappell, who was last seen on board the couple's yacht Four Winds on Australia Day, 2009. His body was never found.

In October, a jury found her guilty and Justice Alan Blow sentenced her to 26 years' jail with a non-parole period of 18 years.

In the Supreme Court in Hobart yesterday, Neill- Fraser's barrister, Michael Croucher, argued the judge should have directed the jury not to accept the prosecution's theory that she used a wrench to kill Mr Chappell while wearing yellow rubber gloves found on board the boat.

Director of Public Prosecutions Tim Ellis, SC, admitted he made a mistake because DNA found on the gloves actually belonged to her son who visited the yacht after Mr Chappell's disappearance and wore the gloves at the request of the police.

But he said it was a "throwaway line" among a volume of evidence against Neill- Fraser.

Neill-Fraser took notes during the hearing, shaking her head often during Mr Ellis's submission and shared brief smiles with her two daughters sitting in the front row of the packed gallery.

The defence also argued that a homeless teenager, who can't be named for legal reasons, should have been recalled to the witness stand after subsequent evidence revealed she had lied about her whereabouts around the time of Mr Chappell's disappearance.

"This is a homeless girl who we don't know, may not be responsible but she may know something about it, she may be connected to people who know," Mr Croucher said.

Mr Ellis said it would have been unfair to subject the girl, who was 15 at the time to more aggressive questioning and the witness could have been recalled by the defence.

Justices Shan Tennent, David Porter and Chief Justice Ewan Crawford reserved their decision until a later date.