Court hears evidence of Irish woman's violent past

 Cathrina Cahill has admitted to killing her former fiance David Walsh.

Cathrina Cahill has admitted to killing her former fiance David Walsh.

A newly-engaged Irish woman who has admitted killing her fiance in Sydney stabbed him in the back of the head more than 18 months before his death, a judge has been told.

Former housemate Isobel Jennings testified that the couple were arguing before she saw Cathrina Cahill come up the stairs with her hand behind her back and then suddenly stab David Walsh in the head three or four times.

Ms Jennings was giving evidence on Thursday at the New South Wales Supreme Court sentencing hearing of Cahill, from Wexford.

Cahill, 27, pleaded guilty at a previous hearing to the manslaughter of Mr Walsh, 29, on the basis of substantial impairment.

She had originally been charged with murder but the charge was downgraded.

Cahill, who is known as Tina, admitted unlawfully killing Mr Walsh - who was also from Wexford - between February 17 and 18 last year in the suburb of Padstow.

She gave psychiatrists a history of being in a traumatic relationship with Mr Walsh, hallmarked by physical, emotional and verbal abuse over a period of time.

Under cross-examination from Cahill's barrister, James Trevallion, Ms Jennings denied lying about the incident in which she said Cahill had stabbed Mr Walsh in October 2015.

The court was told Cahill was charged with one count of reckless wounding of Mr Walsh in relation to him being injured after she threw a large candle at him in November 2015.

She was convicted of the offence in her absence and placed on a two-year bond in April 2016 at Waverley Local Court.

According to the agreed statement of facts, the couple argued on the night of February 17 2017 when they were drinking with others.

They parted, before Cahill, two female friends and Matthew Hyde, a man they had socialised with at one of the pubs, arrived back at the Padstow address where Mr Walsh was either asleep or partially asleep on a couch.

Soon after, Mr Walsh repeatedly attacked Mr Hyde wanting to know who he was and, during the ensuing chaos, Cahill screamed: "Stop it Davey, get off, get off ... he's with Grace."

She tried to get a grip of her fiance's arms when he swung his arm back and she fell to the ground, the facts said.

She moved towards him and punched him in the face with a closed fist, before Mr Walsh pushed her again and tried to punch her in the face.

Eventually, "the offender opened and closed the cutlery drawer quickly taking out a large, very sharp, bladed knife".

One witness said over and over again "put it back" but Cahill replied: "No, he needs to be taught a lesson. It's not fair. Look at poor Matthew."

The hearing is continuing before Justice Peter Johnson.