The Hobart grandmother is serving 23 years' jail for killing partner Bob Chappell, who disappeared off the couple's yacht moored on the River Derwent on Australia Day 2009.

She launched a second appeal against her conviction after a judge decided there is fresh and compelling evidence in the case.

In closing submissions on Wednesday, Neill-Fraser's lawyer Chris Carr SC referenced a report from forensic expert Maxwell Jones provided at an earlier hearing.

"There is a significant possibility that the jury would have delivered a different verdict if the evidence of Mr Jones had been before it," Mr Carr told the Court of Criminal Appeal.

The DNA of then-homeless teenager Meaghan Vass was found aboard the Four Winds yacht.

Ms Vass on Monday told the court she was on the boat the night of the murder and saw a fight between Mr Chappell and other men.

However, she sensationally recanted her story on Tuesday, agreeing that she was "hounded" and "threatened" by people to say she was there.

Neill-Fraser's lawyers have abandoned her evidence, despite earlier calling Ms Vass the crucial witness.

Mr Carr told the court there had been no rational explanation provided at the trial for how Ms Vass's DNA had got on board.

The most reasonable explanation is that she was on the boat at some stage, he added, saying Mr Jones' report articulated "what would have been required" for that DNA deposit to occur.

He said the chance of a secondary DNA transfer was greatly overstated at the trial by the prosecution.

"There was a substantial miscarriage of justice and the appeal should be allowed and a retrial ordered," Mr Carr said.

Crown prosecutor Daryl Coates SC said Mr Jones' report is not substantial, not fresh and could not have led to the possibility that Neill-Fraser would have been acquitted.

He noted the DNA of Ms Vass was swabbed from the boat four days after the January 26 murder.

At least 21 people including a repairman, insurance assessors, civilians, police officers, Neill-Fraser and her family had been on the vessel during the time in between, he said.

Mr Coates said a significant part of Mr Jones' report was "more favourable" to the Crown and "strongly supported" the conclusion that the DNA had been put on the boat a few days before it was swabbed.

The three-judge panel has reserved its decision and could decide to dismiss the appeal, order a retrial or quash the 2010 conviction.

"We have been here before many times. Whilst in some ways a lot rides on this, we will never stop fighting for this case," Neill-Fraser's daughter Sarah Bowles said outside court.

Neill-Fraser, now 67, was found guilty of attacking Mr Chappell, dumping his body in the River Derwent and then trying to sink the boat.

Her first appeal was dismissed by the Court of Criminal Appeal in 2012.

She was granted leave to launch a second appeal under new Tasmanian laws that require "fresh and compelling" evidence to be brought forward.

Australian Associated Press