Gibson is born in Dublin in 1876. Her father, Edward Gibson, is an Irish lawyer and politician who is created Baron Ashbourne in 1886. She becomes a Roman Catholic in 1902.
In 1924, after spending two years in a mental institution, Gibson is released and goes to Rome accompanied by a nurse, Mary McGrath. They take up residence in a convent in a working class neighborhood with a high crime rate. Her crisis of conscience grows as she becomes more convinced that killing is the sacrifice that God is asking of her. During this time she somehow gains possession of a gun.
On February 27, 1925 Gibson goes to her room, reads the Bible, and then shoots herself in the chest. The bullet misses her heart, passes through her ribcage, and lodges in her shoulder. She tells McGrath that she wants to die for God. She recovers from the wound.
On Wednesday, April 7, 1926 Gibson leaves the convent after breakfast. In her right pocket she carries a revolver wrapped in a black veil. In her left pocket she carries a rock in case she has to break a windshield to get to Mussolini. She also clutches the address of the Fascist Party headquarters written on a scrap of envelope as she has read in the newspaper that Mussolini will be there in the afternoon.
Mussolini appears as scheduled and walks through the Palazzo del Littorio, soaking in the praise of the crowd. He stops about a foot from where Gibson is standing. Just before the gun goes off, Mussolini leans his head back to acknowledge the crowd’s adoration and the bullet grazes his nose. Gibson shoots again but the gun misfires.
Mussolini maintains his composure and consoles the crowd saying, “Don’t be afraid. This is a mere trifle.” Gibson is immediately captured and beaten by the crowd. The police gain control of the situation and take her away just before she succumbs to vigilante justice.
At the time of the assassination attempt Gibson is almost fifty years old and does not explain her reason for trying to assassinate Mussolini. It is theorised that Gibson is insane at the time of the attack and the idea of assassinating Mussolini is hers and that she worked alone. In a statement in reply to the questions of the Crown prosecutor, Gibson says she felt impelled by a “supernatural force entrusting her with a lofty mission.”
Gibson is later deported to Britain after being released without charge at the request of Mussolini. She spends the rest of her life in a mental asylum, St. Andrew’s Hospital in Northampton. She dies on May 2, 1956 and is buried in Kingsthorpe Cemetery, Northampton. No one attends her burial.