St. Catherine of Siena: lay, that is, Christian

I didn't know much about St. Catherine before reading Louis de Wohl's Lay Siege to Heaven. I knew that she was Dominican, but I didn't know that she was a tertiary, a lay affiliate of the Dominicans. She is called a nun throughout the book but she lived most of her life in her mother's house. In her letters especially, she urged people in every part of society to move beyond their own interests and embrace catholic peace. At one point, someone describes her as both a politician and a saint. Now, that's what it means to be Christian, or lay.