The former girlfriend of Sydney siege gunman Man Haron Monis has had her sentence for murdering his ex-wife reduced by nearly a decade.

Amirah Droudis, 41, repeatedly stabbed the mother of Monis’s two children in a Western Sydney apartment block in 2013 before dousing her in petrol and setting her alight.

She was sentenced in 2017 to 44 years in jail with a non-parole period of 33 years following a judge-alone trial which concluded that Monis planned the murder but wasn’t prepared to carry it out himself.

On Thursday, the NSW Court of Criminal Appeal quashed the original sentence and imposed one of 35 years with a non-parole period of 26 years.

Droudis’s earliest release date is now March 2041 – about six years sooner than what her original sentence dictated.

The appeal panel, comprised of Chief Justice Tom Bathurst and Justices Clifton Hoeben and Peter Hamill, found the sentencing judge erred when considering the impact of the death of Monis during the Lindt Cafe siege in 2014.

They found the removal of his ongoing “evil and pervasive” influence on Droudis should have been taken into account.

This impacted the ongoing danger she poses and her prospects of rehabilitation, the court found.

Man Haron Monis held 17 people hostage in the Lindt Cafe in Martin Place in 2014.

The judges accepted her killing had a “ritualistic flavour” but said it was not motivated by terrorist ideology.

“There is nothing to suggest that the applicant’s continued adherence to the Islamic faith rendered it more likely that she would engage in future criminal activity of the nature of that for which she had been convicted,” the judgment said.

Monis plotted to murder his former wife to secure custody of their two children after a separation in 2011.

The original sentencing judge, Justice Peter Johnson, described the murder as “a brutal and callous attack upon a defenceless woman”.

He said the “frenzied knife attack” continued despite the 30-year-old victim’s pleas for mercy.

Justice Johnson also found Droudis had ample opportunity to pull out of the plan and ignored Monis’s instructions not to set the victim alight.

Droudis met Monis in 2003 and formed a bond before converting to Islam with her daughter.

She appeared in propaganda videos between 2008 and 2009, reciting scripts written by Monis under the guise of “Sister Amirah”.

Justice Johnson said she had “uncritically adopted and espoused” his “vile beliefs”.

-ABC