MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud (Paris, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - June 19, 1973. 1973. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 7. https://digital.library.emory.edu/purl/470zpc875j-cor.
APA, 6th edition
Chase-Riboud, B. (1973). Letter from Barbara Chase-Riboud (Paris, France) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - June 19, 1973 (Box 1, Folder 7) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/470zpc875j-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud (Paris, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - June 19, 1973.” Letters (correspondence). Barbara Chase-Riboud Papers, 1973. Box 1, Folder 7. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/470zpc875j-cor.