why did robert burn the picture of rowena?

Rowena's picture was something he had clung to in the hope of maintaining her memory. Following the rape he has lost his dignity as well as his treasured sense of privacy. The charity that Findley writes of refers not to Rowena but to Robert himself. By letting go of his sister, he is letting go of the guilt he has carried over her death. Rowena's picture and memory also provided him a sense of comfort, of a time when he was happier and the world made more sense. By destroying her image, Robert is acknowledging that those days are gone and will never return.