MLA
Chase-Riboud, Barbara. Letter from Barbara Chase to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 8, 1958. 1958. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 1. https://digital.library.emory.edu/purl/6214mw6n58-cor.
APA, 6th edition
Chase-Riboud, B. (1958). Letter from Barbara Chase to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 8, 1958 (Box 1, Folder 1) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n58-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - July 8, 1958.” Letters (correspondence). Barbara Chase-Riboud Papers, 1958. Box 1, Folder 1. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n58-cor.