London teenager found guilty of plot with all-female terror cell
Safaa Boular, 18, plotted the grenade and gun attack in her home town after the authorities intervened to stop her travelling to Syria to marry an IS fighter she had met online.
She is the youngest female to be charged with planning an IS attack in Britain.
Boular was only 16 when she made contact with British-born IS fighter Naweed Hussain, 32, discussing marriage and how they would don his-and-hers suicide belts.
But her hopes of joining him were thwarted when she was stopped at the airport in August 2016 following a family trip to Morocco, and her passport was confiscated.
Instead Boular decided to plan an attack in Britain, detailing it in coded language - grenades were "pineapples" - to online contacts who were in fact undercover agents.
Hussain was later killed in a drone strike.
When Boular was charged with preparing terrorist acts in April 2017, she passed the baton to her sister Rizlaine, 22, and their mother Mina Dich, 44, who hatched their own plan.
The trio were taped talking about an Alice in Wonderland -themed tea party, which the prosecution argued was code for an attack.
Rizlaine and her mother were arrested after being tracked by police visiting potential sites around Westminster and buying knives.
They pleaded guilty to terror offences, along with a fourth woman, Rizlaine's friend Khawla Barghouthi, 21, who later admitted failing to alert the authorities.
Safaa Boular denied the plot but was found guilty on Monday after a trial.
Dean Haydon, Britain's top counter-terror police officer, said the plot "involved a family with murderous intent, the first all-female terrorist plot in the UK connected to Daesh (IS)".
"All three women were filled with hate and toxic ideology and were determined to carry out a terrorist attack," he added.
"Had they been successful, it could well have resulted in people being killed or seriously injured."
Rizlaine, her mother and their friend will be sentenced on June 15, although a date has not yet been set for Safaa Boular's sentencing.
In April, French President Emmanuel Macron warned that militants "use all contemporary forms of financing" in an address at the closing of a two-day conference on combating the funding of terror groups at the Organisation for Economic Cooperation and Development (OECD), which brought together around 80 ministers and 500 experts.
"We have to cut off terrorism at its roots: it feeds on human trafficking, drugs and weapons. There's always an underlying economy," said Macron, urging global "transparency and mobilisation."
"We have to cross to a new stage in the fight against Daesh and al-Qaeda," he said, using the Arabic acronym for the Islamic State militant group.
A French presidential official briefing journalists ahead of the terror funding conference this week said that IS income was estimated at about one billion dollars (820 million euros) a year between 2014-2016.
Most of this was from local taxation, oil revenues and looting, with far smaller amounts flowing in from overseas donors.
IS swept across large parts of Syria and neighbouring Iraq in 2014, declaring a cross-border "caliphate" in areas they controlled.
Syrian and Iraqi forces have since driven IS from nearly all the territory it once held, except for a small presence in the remote desert areas along the border.
But French officials are concerned that the money has been transferred out of Syria and Iraq and could be used to rebuild the organisation.
"It has been moved since, at least in part. It's probably somewhere," the official said on condition of anonymity. These groups are very skilful in using sophisticated techniques to move financial resources around."