A young girl of unknown origin who works as a prostitute. A mute from birth, Isabelle has a gentle and submissive personality, as well as a "purity" that Étienne immediately notices. The Children's Crusade meet her during their travels, and she quickly turns to worshiping Étienne. Her and Etienne fall in love, and Isabelle runs away from her town to follow him. The two later become lovers, which is the final straw in Étienne being deemed a heretic. While making love to Étienne, she was stabbed in the back by Christian and fell into the river to bleed. Post-story, she bears Étienne's child and finds new purpose in life serving God.