Greek coroner Ilias Bogiokas, who conducted the autopsy on Ms McNamara's body, said the body did not have any injuries but that the final cause of death will not be announced until the lab tests are completed, which could take a month or more.
Meanwhile, as her family and friends wait for answers, heartless trolls have targeted the young model's social media profiles, blaming her for her death.
"She is dead because of her bad choices and the company she held," one commenter said.
"You lived for attention, now you've got it," another added.
Her photos have been flooded with comments suggesting she worked in the sex industry and "got what she deserved".
But supporters and friends among her 32,000 Instagram followers rallied to her defence, trying to drown out the trolls.
"To all the horrible people thinking she did anything bad she hadn't done a bad thing in her life this girl. She was best friends with my older brother and I've never known a sweeter girl. Yes she showed off her body but why wouldn't she? Girls are told to love your body exactly as it is. And that's what she did. She loved every thing about the world including herself," one friend wrote.
"These comments simply say to me loud and clear that the vast majority of people not only lack common decency but are moronic, lacking in empathy and willing to make up ridiculous unfounded stories about someone they didn't know. My sincere condolences to her family. It must be heartbreaking. Who cares what she was doing? It was her life and now her family are suffering. It is that simple and beyond that none of our business. Enough said," another said.
Ms McNamara, from Port Macquarie, had been working for four months as a stewardess on the six-storey vessel owned by Mexican mining mogul and billionaire Alberto Bailleres.
She was on her last shift and was planning to meet up with her mother and sister, who had been on their way to Greece at the time.
The young model had been looking forward to their visit, posting an upbeat message on social media just days before her death.
"Happy birthday to the most amazing big sister I could ever ask for, 5 days till I get to see you!!! Excitement is an understatement", she wrote.
That post was in stark contrast to an earlier, cryptic message that appeared on Ms McNamara's Instagram page.
"My head is all over the shop today," she wrote, along with emojis of a volcano, a tornado and a needle with blood dripping from it.
And sharing an image of herself on a quad bike, she added: "Take me back to this where my only worry was not cracking my skull open."
But in a chilling development, it has been reported that Ms McNamara made a distressing phone call to her family, just moments before she was fatally injured on a superyacht, to report an "incident" with another crew member.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
