MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud (Milan, Italy) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 11, 1963. 1963. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 3. https://digital.library.emory.edu/purl/822h70rzr5-cor.
APA, 6th edition
Chase-Riboud, B. (1963). Letter from Barbara Chase-Riboud (Milan, Italy) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 11, 1963 (Box 1, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/822h70rzr5-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud (Milan, Italy) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 11, 1963.” Letters (correspondence). Barbara Chase-Riboud Papers, 1963. Box 1, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/822h70rzr5-cor.