AN IRISH WOMAN who killed her fiance in Sydney has been sentenced to eight years in prison.

Justice Peter Johnson found Cathrina Cahill had suffered a “loss of control” associated with the mental condition she suffered due to their “unusual and abusive relationship”.

For newly-engaged Cathrina Cahill, known as Tina, her fiance’s jealous and violent attack on a male guest in their Sydney home was “the last straw”, the court heard.

The 27-year-old was again confronted with David Walsh’s drunken rage and reacted by taking out a large, very sharp knife from the cutlery drawer and fatally stabbing him once in the neck.

The couple had behaved aggressively towards each other during their “volatile” two years together, which culminated in their engagement six weeks before the stabbing.

The New South Wales Supreme Court judge jailed Cahill for eight years with a non-parole period of five years, noting she was expected to be deported to Ireland on her release.

The 27-year-old had pleaded guilty to the manslaughter of Walsh, 29, who was stabbed in the early hours of 18 February 2017, at the Padstow home they shared with two other Irish nationals.

The plea was based on substantial impairment due to an abnormality of the mind.

“I am satisfied the psychiatric evidence supports the existence of significant depression on the part of the offender at the time of the killing which arose from the unusual and abusive relationship with Mr Walsh,” the judge said.

He referred to the “history of aggression and verbal abuse” by Mr Walsh.

“On occasions, the offender had responded or retaliated herself with violence, including the use of a knife to injure him,” the judge said.

But he was satisfied that her violence was triggered by, or responsive to, acts of violence or anger by Walsh.

The fatal attack occurred when an intoxicated Walsh launched an unprovoked attack on Mathew Hyde, who had been invited into the home by Cahill and the two other female housemates after they met him at a pub.

“Mr Walsh was attacking the unfortunate Mr Hyde upon the mistaken basis that he may have demonstrated some interest in (Cahill).”

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A housemate repeatedly told Cahill to put the knife back in the drawer, but she said:

No, he needs to be taught a lesson. It’s not fair. Look at poor Mathew.

At the time, she was on a good behaviour bond and the subject of an apprehended violence order issued to protect Walsh, after she was convicted of recklessly wounding him with a glass candle holder in 2015.

The judge accepted Cahill’s evidence about his repeated violence, including punching strangers and biting her all over her body and his accusations of her sleeping with other men.

Despite his controlling and demeaning conduct, Cahill testified she had “loved and adored” him and believed him when he promised to change.

Victim impact statements prepared by Walsh’s relatives in Ireland “reflect the enormous loss suffered by each of them” and the “terrible news of his death” received by them from a distant land.

The judge accepted Cahill was remorseful and found she had “excellent” rehabilitation prospects.