Neill-Fraser is serving 23 years' jail for the murder of partner Bob Chappell, who disappeared off the couple's boat moored on the River Derwent on Australia Day 2009.

But she has always maintained her innocence and on Monday began a landmark appeal in the Supreme Court in Hobart.

The DNA of then-homeless teenager Meaghan Vass was found on the Four Winds, but she told the original trial she had never been onboard.

Ms Vass has since changed her story, signing an affidavit to claim she was on the yacht along with some men.

She was asked by Robert Richter QC, Neill-Fraser's lead lawyer, whether she was there the night Mr Chappell went missing.

"Yes," she told the court.

Mr Richter acknowledged Ms Vass had a history of giving conflicting accounts and had in 2012 said she "had never been on a yacht in her life".

Ms Vass told a former lawyer of Neill-Fraser in 2017 that she had been on the boat but was too scared to give further details, he said.

"The credibility issue is secondary to whether or not the DNA was deposited by her presence being on the boat on Australia Day," Mr Richter said.

Mr Richter said only Ms Vass could answer the question of whether she was on the yacht when Mr Chappell was killed.

She is scheduled to give further evidence at the five-day hearing when it resumes on Tuesday.

Neill-Fraser, 66, was a few years ago granted leave to launch a second appeal against her conviction after convincing a judge there was "fresh and compelling" evidence not heard at the trial.

The current three-judge panel could decide to order a re-trial or quash her 2010 conviction.

Neill-Fraser's first appeal was dismissed by the Court of Criminal Appeal in 2012.

Australian Associated Press