Amirah Droudis, 37, will spend at least 33 years behind bars for killing the woman -who cannot be identified - in 2013.
Droudis's boyfriend, Man Haron Monis, took 18 people hostage in a Lindt cafe in central Sydney in 2014.
The 16-hour siege ended with the deaths of Monis and two hostages when police stormed the building.
Monis had been charged with being an accessory to his ex-wife's killing, and was on bail at the time of the siege.
The Supreme Court of New South Wales heard that Monis planned the 2013 murder and Droudis carried it out.
The victim, identified by the pseudonym Helen Lee, was stabbed 18 times before being doused in petrol and set alight outside an apartment in western Sydney.
After the trial, Justice Peter Johnson ruled that Monis recruited Droudis to murder his ex-wife.
"The offender uncritically adopted and espoused Monis's foul beliefs and acted in public support of him in public protests," he said in his sentencing remarks on Wednesday.
The judge described Monis as "an evil man" whose death was "a result of his own criminal and murderous acts".
"No-one mourns his passing and many have been left to grapple the consequences of his destructive acts," he said.
The judge acknowledged claims that Droudis had been repeatedly assaulted by Monis.
Droudis was sentenced to a maximum 44 years in jail with a non-parole period of 33 years.
Detective Inspector Jason Dickinson, who worked on the case, said he was satisfied with the sentence handed to Droudis.
"This was a brutal and callous crime and I think the sentence today has reflected that brutality," he told the Australian Broadcasting Corp.
The victim's family made a statement outside court, thanking the judge, prosecutors and police.
"Today we are very happy that justice has been served to our only daughter," the statement said.
The findings of an inquest into the cafe siege are due to be handed down this year.
How the Sydney siege unfolded

Pieces from the board game, which hasn't been played for 1,500 years, have been found in Qingzhou City in China.
Archaeologists found a 14-faced dice made of animal tooth with ancient Chinese writing on it.
They also discovered 21 game pieces with numbers painted onto them, as well as a broken tile decorated with two eyes.
The game is said to be called "bo", but researchers are unsure how it was played.
The tomb was built to bury rich Chinese people around 2,300 years ago.

Chronic myeloid leukaemia (CML) patients are often required to take tyrosine kinase inhibitors (TKIs) indefinitely.
But 93% of those in a new study stayed cancer-free after stopping or reducing treatment.
Cancer Research UK said the results were "promising" but dosages should not be changed without a doctor's advice.
In 2000, trials of TKIs proved successful in controlling the rare disease, but also had side-effects,  including an increased risk of infection, skin rashes, nausea, hair loss and in some cases hormone disorder and a build of fluid around the heart.
The follow-up study, led by the University of Liverpool and involving consultants from Newcastle's Freeman Hospital, saw patients being given half the standard dose for the first 12 months. If leukaemia levels remained low, the drug was then stopped completely.
So far, out of 174 patients tested, 93% have shown no evidence of their leukaemia relapsing one year after reducing their dosage and many reported a significant decrease in side-effects within the first three months.
Source: CML Support
Dr Wendy Osborne, who is leading the Destiny study in Newcastle, said: 'We've gone from having patients with a potentially incurable disease and requiring toxic chemotherapy and transplantation, to now selecting some patients, again in a clinical trial setting, to stop the drug completely to remove any side-effects they have.
"This in itself is moving towards saying we've cured some patients and this is all because of research."
Dr Ã
The girlfriend of a man behind a deadly siege in a Sydney cafe has been jailed for murdering his ex-wife.
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An ancient board game has been found in a Chinese tomb.
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New research could see patients with a rare blood cancer live longer without the side-effects of drugs, doctors say.