Pat Stacy Donahugh, 53, companion to John Wayne who wrote a book about their years together. Before her marriage to Richard Donahugh in 1982, Pat Stacy worked as an assistant to the fabled actor and became his companion in the last years of his life. She later published her book, "Duke, a Love Story." A native of Louisiana, she graduated from Northeast Louisiana University and became a teacher. Moving to California, she worked for the Arthur Andersen Co. accounting concern in Beverly Hills and then for Wayne. After his death, she became an aide to Donald L. Bren of the Irvine Co. On Thursday in Newport Beach of lung cancer.