The papacy had been at Avignon for seventy years, and Catherine made its return her cause. She wrote to Gregory XI repeatedly, went to Avignon in person in 1376 as an envoy of Florence, then at war with the papacy, and pressed him directly. He returned to Rome in 1377. How much of that was her doing is argued, since the political pressures were considerable, but she was in the room.
What followed was the catastrophe of her life. Gregory died in 1378, the election of Urban VI was disputed, a rival was chosen, and the Western church split into two obediences with two colleges of cardinals for the next forty years. Catherine spent her remaining two years in Rome campaigning for Urban, writing to every ruler in Europe to hold them to his obedience, while writing to Urban himself about his violent temper and warning him that he was losing men by it. She had helped bring back a papacy that promptly fractured.
She died in Rome in 1380, at thirty three, worn out and by her own description having offered her life for the church. The Dialogue, dictated in 1378, is her one systematic work: a conversation between a soul and God built on the image of Christ as a bridge over a flood. She was canonised in 1461, named a Doctor of the Church in 1970 alongside Teresa of Avila, the first two women given the title, and made a patron of Europe in 1999.