"There is no doubt that Mr Jones died from the stabbing ... the question is whether Miss Gerbes is criminally responsible for his death," Justice Goddard said.
She acknowledged the jury had to consider if the stabbing was accidental or if there was a "reasonable possibility of self-defence".
"This is a tragic case. A young man has been killed and a young woman is on trial for manslaughter," she told the jury.
Yesterday, forensic pathologist Martin Sage, who carried out a post-mortem examination on Mr Jones said the single stab wound resulted in "torrential bleeding" and an unrecognisable blood pressure when Mr Jones reached hospital.
Napier CIB Detective Phil Sayers also gave evidence yesterday, which included Gerbes' interviews with police and a video reconstruction of the fatal events.
The night Mr Jones died, Gerbes said the pair had been fighting.
Throughout the trial Gerbes said Mr Jones inexplicably grabbed her hands and pulled the knife towards him.
Gerbes broke down in tears as the verdict was read, as did the large group of her supporters sitting in the public gallery.
"It's been bloody hard on her," her mother said.
A family member of Mr Jones also yelled abuse and accusations from the gallery at Gerbes as the verdict came through.
