MLA
Chase-Riboud, Barbara. Letter from Barbara Chase (SS Flandre) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - October 4, 1957. 1957. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 1. https://digital.library.emory.edu/purl/6451g1jxq4-cor.
APA, 6th edition
Chase-Riboud, B. (1957). Letter from Barbara Chase (SS Flandre) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - October 4, 1957 (Box 1, Folder 1) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6451g1jxq4-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase (SS Flandre) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - October 4, 1957.” Letters (correspondence). Barbara Chase-Riboud Papers, 1957. Box 1, Folder 1. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6451g1jxq4-cor.