The Londoner, 17, allegedly wed Naweed Hussain, 30, online in September 2016 after she was unable to join the terrorist in Syria.
Together they planned an atrocity where she would use “pineapple” hand grenades and a pistol to slaughter civilians, Westminster Magistrates’ Court heard.
Hussain, a British Pakistani from Coventry, travelled to Syria in June 2015 after ditching his first wife and family.
The jihadi was recently killed in the ISIS stronghold of Raqqa, Syria and his “wife” is then thought to have taken over the terror plot.
She is accused of requesting hand grenades – dubbed “pineapples” – and a Russian semi-automatic Tokarev pistol.
She allegedly targeted the British Museum and tried to recruit others to the attack.
Prosecutor Karen Jones told the court on Tuesday: “She intended to carry out a terrorist attack in the UK…she having a desire to be become a martyr.”
The teen – who cannot be named for legal reasons – pleaded not guilty to committing acts of terrorism between December 1 last year and April 12 last year.
A trial is scheduled for August 11.