MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - April 20, 1979. 1979. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 8. https://digital.library.emory.edu/purl/39995x6bmh-cor.
APA, 6th edition
Chase-Riboud, B. (1979). Letter from Barbara Chase-Riboud to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - April 20, 1979 (Box 1, Folder 8) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/39995x6bmh-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - April 20, 1979.” Letters (correspondence). Barbara Chase-Riboud Papers, 1979. Box 1, Folder 8. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/39995x6bmh-cor.