Sydney cousin stabber should 'rot in jail'

The family of a Sydney woman stabbed to death by her cousin after a fight over a luxury car hopes she "rots in jail".

Katherine Abdallah was found guilty in December at her retrial of the manslaughter of 21-year-old Suzie Sarkis in 2013.

On Tuesday, a judge shaved one-and-a-half years off her original prison term in sentencing her to a non-parole period of six years and nine months.

"I hope she rots in jail," Ms Sarkis' sister Christine told reporters outside the NSW Supreme Court.

"I will never forgive her. I will never forget."

The cousins had been fighting over Abdallah's new $184,000 Mercedes before she armed herself with two knives and killed her younger relative at her Brighton-Le-Sands townhouse on February 9, 2013.

The night before the death, Abdallah told police "she's going to be in serious trouble when I get her" for driving the car at high speed without permission and damaging the front wheel.

"You guys will probably be called back," she added in what proved to be an eerily accurate prediction.

Abdallah initially told officers the culprit was a fictitious Lebanese woman before claiming self-defence once CCTV footage was found.

She also lied to a triple-zero operator saying she was applying pressure to Ms Sarkis' deep chest wound when she was in fact carefully cleaning the knives.

Abdallah remained stony-faced on Tuesday as Justice Julia Lonergan handed her a maximum nine years behind bars.

But the 36-year-old wiped her eyes as the judge condemned her for betraying the woman she used to call her "baby sister".

"This terrible crime has torn the family apart," Justice Lonergan said.

The court had previously heard the grieving brother of Ms Sarkis had to visit her grave on his wedding day last year so she could be part of the celebration.

Christine Sarkis fought back tears as she stood with her pregnant sister-in-law outside court, saying their loss had taken a devastating toll.

"She can't be an aunty to her nephew that's coming," Ms Sarkis said.

"My sister is in heaven, she's our angel, and (Abdallah's) family have to deal with her being a murderer."

Abdallah originally faced a murder trial but was found guilty of the less serious charge of manslaughter and jailed in May 2015 for at least eight years and three months.

Later that year she successfully challenged her conviction and was ordered to face a second trial. She was released on bail in February 2016.

Since going back into custody Abdallah, who has a history of cocaine abuse, has committed a string of offences behind bars including drug possession.