MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud (La Chenillière, Pontlevoy, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 15, 1969. 1969. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 6. https://digital.library.emory.edu/purl/955m905rc9-cor.
APA, 6th edition
Chase-Riboud, B. (1969). Letter from Barbara Chase-Riboud (La Chenillière, Pontlevoy, France) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 15, 1969 (Box 1, Folder 6) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/955m905rc9-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud (La Chenillière, Pontlevoy, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 15, 1969.” Letters (correspondence). Barbara Chase-Riboud Papers, 1969. Box 1, Folder 6. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/955m905rc9-cor.