A "triggered" Freedom Mona Maunsell Anderson felt Nicholas Braid was lying to her about his name before fatally stabbing him on the Gold Coast, a court has heard.
Anderson later told an undercover officer that she did not usually carry a knife, preferring to use her fists, a Brisbane Supreme Court jury was told on Wednesday.
But Anderson told the officer she had a "particular grievance" with Mr Braid and had a knife in her bag when she and an associate met the 35-year-old outside a Gold Coast apartment building in April 2020, the court heard.
"You will hear the killing was an expression of some grievance that she held at the time," crown prosecutor Stephen Muir said.
"The accused identifies a particular grievance that she had with the deceased.
"She felt like he was lying to her about his name immediately prior to the incident."
CCTV footage captured the moment Anderson, now 23, stabbed Mr Braid "with some force" before he stumbled and lowered himself to the pavement, Mr Muir said.
Mr Braid died at a Gold Coast hospital about half an hour later.
He suffered a 13cm deep stab wound, puncturing his main artery.
Anderson was arrested the next day after police found the clothing she was wearing at the time of the stabbing - including distinctive red shoes - in a garbage bag.
The knife was never found.
Anderson pleaded guilty to manslaughter but it was rejected by the prosecution.
She is on trial for murder.
"What was in the accused's mind when she stabbed the deceased in the middle of his chest - it's your determination of that question which will decide this trial," Mr Muir told the jury.
A key insight into Anderson's state of mind at the time would be presented by an undercover officer's evidence, he said.
The officer was placed in the Southport watchhouse with Anderson the night of her arrest.
In the recorded conversations, Mr Muir said Anderson told the officer she and an associate met with Mr Braid to "sort out a situation" with the 35-year-old.
"You will hear that the accused was triggered prior to the killing," he said.
"She explains she doesn't usually carry a knife, preferring to use her fists, but on this particular occasion she said she was either going to kill someone or herself."
He said Anderson also discusses her drug use.
Defence barrister Jacob Robson said Anderson had admitted her responsibility by pleading guilty to manslaughter.
"She had no excuse and no lawful reason to do what she did in that moment ... this trial is about your assessment of her intention in that moment," he said.
"This is not a case where violence is explained by some intense, longstanding animosity ... it's senseless."
Mr Robson said intoxication was not an excuse for the stabbing.
"But it comes into play as you are assessing someone's intent, consider whether it clouded her judgment ... (and) how it affects their co-ordination," he said.
