The jury was told on Monday an argument started when the pair returned home from a party at a friend's house. The fight grew violent, with slaps and punches being thrown and Mr Jones choking Gerbes.
Crown Prosecutor Clayton Walker said there was no dispute, the knife was picked up and held by Gerbes in the moments before the fatal wounding occurred.
He said the Crown did not accept the wound was self-inflicted.
In the interview, Gerbes told police she didn't know why she had picked up the knife. "I wasn't trying to hurt him, maybe I was trying to be threatening or maybe it was as a joke ... As a stupid action I just picked it up, I wasn't aiming it at him ..."
Gerbes said she would have picked up a spoon and held it to him if it had been the closest thing to her.
She said Mr Jones was trying to be intimidating in the minutes before the incident, pushing her into a corner and she "just wanted him to stop". She said she could not remember what they were arguing about in the minutes before the incident but that she did not want to be pushed around and wanted him to "back off".
"He just grabbed me around the wrist, around the hand, he just pulled straight towards him, maybe he was trying to get it off me and I let go of it I don't know."
She said his face "dropped".
" ... he went all white, he was real worried, the only words he said to me were 'call an ambulance I'm not joking'."
A forensic pathologist, who gave evidence yesterday, said a knife had perforated Mr Jones' major artery and caused "torrential bleeding".
He died hours later at the Hawke's Bay Hospital.
The detective put it to her that it did not add up. He asked if the arguing and the violence towards her in the minutes prior to the incident was enough to make her "snap" for just one second.
Gerbes said the relationship had been a good one but with "rough patches" and "drama" throughout the year they had been living together.
"We've had decent-sized arguments about relatively important stuff in the year we've been together but we always find a way to make it up ... regardless of all the crap that's gone on we don't want to risk losing each other."
She told police about an earlier incident in which both her and Mr Jones ended up with black eyes.
She said Mr Jones had hit her head into the ground and thrown her around before punching her in the face.
Gerbes said Mr Jones could not remember the incident in the morning and she chose not to report it to the police as it would be "hypocritical" given she had also punched him.
A witness for the defence, the mother of one of Gerbes' friends, said it was the worst black eye she had ever seen.
She said she was concerned for Gerbes' welfare.
"The time she came round to my house with a black eye, a swollen face, there was no white left in her eye. It was one of the worst black eyes I've ever seen."
The witness said she had also seen bruising and finger marks around Gerbes' neck as well as a severe bruise on her buttock.
In a second police interview, recorded the following month and played to the jury yesterday, Gerbes said her parents were not happy with her and Mr Jones' relationship.
"They thought it was abusive ... they thought one of us would end up seriously hurt."
Gerbes' brother also gave evidence and said he had witnessed two violent incidents between the pair. One when Mr Jones had his hand around her throat and one when he was gripping her firmly around the arm.
He said he was aware of one incident where Gerbes had been violent towards Mr Jones.
The trial is expected to end tomorrow.
