Catholic Schools Week at San Gabriel Mission High School began with a Catholic identity Assembly and the dynamic guest speaker, Sister Helen Prejean. She is the author of Dead Man Walking, her most talked about book that was made into a play, an opera, and a major motion picture starring Susan Sarandon and Sean Penn. Catholic Schools Week at San Gabriel Mission High School began with a Catholic identity Assembly and the dynamic guest speaker, Sister Helen Prejean. She is the author of Dead Man Walking, her most talked about book that was made into a play, an opera, and a major motion picture starring Susan Sarandon and Sean Penn.