Safaa Boular, 19, planned an attack with grenades and guns on the British Museum in London after her attempt to become an Islamic State (IS) suicide bomber in Syria was thwarted.
She and Hussain planned to carry out a suicide bomb attack in Syria but she was prevented from joining him after having her passport seized.
Instead of committing a terror attack in Syria, she discussed a grenade and gun attack on the British Museum – which she continued plotting after Hussain was killed in a drone strike in April 2017.
She was arrested after the plans were uncovered by MI5 role-players and the Boular family home in Vauxhall, south London, was bugged.
While in prison on remand she discussed further plans for a terror attack with her sister Rizlaine Boular, 23, using coded language by pretending to talk about preparations for an innocent Mad Hatter’s tea party.
Along with her mother and older sister she was a member of the UK’s first all-woman terror cell.
She was jailed for life with a minimum term of 13 years at the Old Bailey in August
But her tariff was reduced to 11 years at the Court of Appeal in London on Tuesday.
Lord Justice Holroyde, sitting with two other judges, said the original term was too long in light of her youth and the fact she had been subjected to indoctrination from the age of 12.