(CNN)A British teenager was found guilty Monday of plotting a terror attack on the British Museum in London as part of an all-female ISIS cell.
Safaa Boular, 18, planned the attack after police foiled her plans to marry an ISIS fighter in Syria, according to statements by the Crown Prosecution Office (CPS) and London's Metropolitan Police. Her sister, mother and a friend all pleaded guilty to terrorism offenses at an earlier hearing.
"Safaa Boular's intention was to cause serious injury and death. She planned to do this in Syria by detonating a suicide belt with her fiancé by her side," said the head of the Crown Prosecution Service's counterterrorism division, Sue Hemming.
"When she was prevented from travelling, her focus switched to an attack on the British Museum where there would be a large crowd," said Hemming.
Boular used references to the tea party scene in Alice in Wonderland when she concocted the plot, according to the Press Association.
She was stopped by police at Stansted airport, north of London, and admitted to plans to travel to Syria to join ISIS fighter Naweed Hussain. She said she wanted to support a suicide attack he was plotting while the pair held hands.
After her travel plans were thwarted, she continued to chat with Hussain online and set plans in motion to carry out an attack on the British Museum using grenades and firearms. Hussain was killed on April 4, 2017. After his death, Boular sent a message to someone she considered an ISIS supporter asking for "martyrdom for his sake."
She and her sister, Rizlaine Boular, 22, talked about planning a "party" on April 27, 2017, which the prosecution argued was code for terror attack. The plan was supported by her mother and friend, according to the CPS.
"They all present a danger to the public and will be sentenced for their actions," said Hemming.
She is the youngest female charged with planning an ISIS attack in the country, according to the Press Association.
Last week, a British ISIS supporter admitted to calling on jihadis to attack 4-year-old Prince George. Husnain Rashid, 32, wrote messages online encouraging militants to carry out attacks, including posting a picture of Prince George next to a superimposed silhouette of a jihadi fighter, the CPS said.