LONDON (AP) — An 18-year-old British woman has been sentenced to a minimum of 13 years in prison for plotting to attack the popular British Museum in London after failing in her ambition of becoming a jihadi bride in Syria.

Safaa Boular was convicted in June of preparing terrorist acts. Her mother and sister were also convicted — Britain's first case involving an all-female Islamic State group-inspired cell.

Prosecutors said Boular plotted a grenade-and-gun attack in messages with an older IS fighter in Syria whom she hoped to marry. He was killed in 2017.

Passing sentence Friday, judge Mark Dennis said although Boular was young, "she knew what she was doing and acted with open eyes."

Boular's sister, Rizlaine Boular, and mother, Mina Dich, pleaded guilty to terrorism charges and were sentenced earlier.