MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud (London, England) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - September 15, 1985. 1985. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 9. https://digital.library.emory.edu/purl/354xgxd31r-cor.
APA, 6th edition
Chase-Riboud, B. (1985). Letter from Barbara Chase-Riboud (London, England) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - September 15, 1985 (Box 1, Folder 9) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/354xgxd31r-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud (London, England) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - September 15, 1985.” Letters (correspondence). Barbara Chase-Riboud Papers, 1985. Box 1, Folder 9. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/354xgxd31r-cor.