Adel Kermiche, 19, murdered Father Jacques Hamel, who was in his 80s, during a morning mass in July.
Kermiche and his accomplice Abdelmalik Petitjean were then shot by police as they left the church in Saint-Etienne-du-Rouvray, Normandy, using nuns as human shields.
On Friday, Paris prosecutor Francois Molins said the detained woman, referred to as Sarah H, was also betrothed to another extremist who carried out a deadly attack in June.
Larossi Abballa killed two police officials in Magnanville and filmed the aftermath on Facebook Live before being shot dead in a raid on his home.
Sarah H’s current fiance was arrested on Thursday, Mr Molins said.
She and two other females – one a teenager – were detained after a car full of gas cylinders was discovered close to Notre Dame Cathedral in the French capital on Sunday morning.
The Peugeot 607 also contained three jerry cans of diesel and was found with its hazard lights on.
The three women are accused of planning to attack a railway station in Paris this week.
Mr Molins said the suspects were guided by Islamic State (IS) commanders in Syria.
“The terrorist organisation uses not only women, but young women, who get to know them and develop their plot from a distance,” he told a news conference.
An interior ministry statement said: “An alert has been issued to all stations but they had planned to attack the Gare de Lyon on Thursday.”
The youngest of the women, Ines Madani, 19, is said to have written a letter pledging allegiance to IS.
Shouts of ‘Allahu Akbar’ – Arabic for God is Greatest – can be heard on video footage of the women’s arrests.
Madani apparently stabbed a police officer in the leg before being shot and wounded. She is being treated in hospital.
TV footage showed a policeman leaving the scene of the arrests on the outskirts of Paris carrying a large knife.
The wounded officer’s injuries are not life-threatening.
Interior minister Bernard Cazeneuve said: “These three women aged 39, 23 and 19 had been radicalised, were fanatics and were in all likelihood preparing an imminent, violent act.”
French President Francois Hollande said: “A group has been destroyed, but there are others. Information we were able to get from our intelligence services allowed us to act before it was too late.”
In all, five women and two men, one with ties to Abballa, have been arrested in connection with the plot.
Madani’s father was detained and later released after reporting his daughter had gone missing with the Peugeot car.
News Source SkyNews