Rachel Joyce offers something rare in “The Love Song of Miss Queenie Hennessy.” The book is neither a prequel nor a sequel but a companion book to her moving 2012 debut, “The Unlikely Pilgrimage of Harold Fry.” In that first novel, Harold Fry, a retired Englishman, received a letter from a former colleague, Queenie Hennessy, who told him she was dying of cancer.