Meaghan Vass tells court what happened the night Bob Chappell disappeared from his yacht

Neill-Fraser is serving 23 years' jail for the murder of Mr Chappell, of which she has served more than a decade.

Meaghan Vass appeared briefly by videolink in the Hobart Supreme Court on Monday morning for the first day of a week of hearings.

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She was asked by Neill-Fraser's senior defence counsel, Robert Richter, if she was onboard the Four Winds yacht the night Neill-Fraser's defacto partner Bob Chappell disappeared on Australia Day 2009, to which she replied "yes".

The hearing was adjourned early on several occasions to allow Ms Vass to seek legal advice on her giving evidence.

Justice Helen Wood, who is part of a panel overseeing the hearings with Justice Robert Pearce and Justice Stephen Estcourt, explained evidence given by Ms Vass in these proceedings could not be used against her in other proceedings.

But she said if Ms Vass provided false statements to the court, action could be brought against her in these proceedings.

In his opening remarks, Mr Richter said there were two central issues to Neill-Fraser's appeal case: whether Ms Vass was onboard the Four Winds the night Mr Chappell disappeared and whether Neill-Fraser was also onboard and played a role in the disposal of his body.

"There is, as we say, one witness that can answer these questions and that is Megan Vass," he said.

Ms Vass' DNA was found onboard the Four Winds through forensic analysis.

In the 2010 trial, Ms Vass denied she had been on the yacht and the prosecution argued the DNA must have shown up there through secondary transfer.

Mr Richter told the court it was pure speculation and guesswork as to how the DNA could have been present on the yacht if Ms Vass hadn't been there.

He told the court she made contradictory statements in four statutory declarations about the night of January 26, 2009 - two of which denied her presence on the yacht and two which stated she was on the yacht with others.

But Mr Richter said her credibility as a witness should not be questioned over the presence of her DNA. "The real question is not whether she is an unreliable witness ... but whether there is fresh and compelling evidence," he said.

In her evidence on Monday afternoon, Ms Vass said she had been with her boyfriend Sam Devine and his friend Stephen Gleeson on the night of Mr Chappell's murder.

Ms Vass, who was 15 years old at the time, said Mr Devine and Mr Gleeson had been drinking at Goodwood when they decided to travel to Sandy Bay to rob boats to get more money for alcohol.

"The boys were knocking off boats and whatnot and I just tagged along being the girlfriend," Ms Vass said.

She said the three found a dinghy on a beach at Sandy Bay and rowed out to the Four Winds.

Ms Vass said they boarded the yacht, believing nobody was onboard.

She said an argument started when Mr Chappell confronted them.

Bob told Sam and that to get off the boat," Ms Vass said.

"That's when Samuel started flipping. He got a bit angry and lashed out. I can remember is seeing a lot of blood."

She said the sight of the blood made her panic and she vomited on the deck of the boat.

Under questioning from the Director of Public Prosecutions Daryl Coates, Ms Vass told the court she had been homeless at the time of the murder and had been mostly homeless since that time.

She said she had battled drug addiction since 2009 which she had recently overcome.

Ms Vass said she had been forced to live off little money over the past decade, and on occasion, had to steal to eat.

She said she had problems with her memory at times and could not recall all of the events on January 26, 2009.

Ms Vass said she did not see the entire argument between Mr Chappell and the men onboard the board as some of it occurred below deck.

"I could hear it unfolding," she said.

Mr Richter and Mr Coates earlier in the hearing objected to Ms Vass having a support person, friend Andrea Brown, next to her while she was giving evidence in the virtual witness box.

Mr Richter said he was prepared for Ms Brown to remain in the room if it meant evidence could be obtained from Ms Vass but said an independent support person provided by the court would be more appropriate.

Ms Brown did not reappear in the room after the lunch break.

Throughout her time on the stand, Ms Vass became highly distressed under questioning, repeatedly asking when she would be able to go home.

Justice Wood called an adjournment until 9.30am on Tuesday when Ms Vass said she was no longer in a state to give evidence.