MLA
Chase-Riboud, Barbara. Letter from Barbara Chase (Paris, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 20, 1961. 1961. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 2. https://digital.library.emory.edu/purl/713905qgrp-cor.
APA, 6th edition
Chase-Riboud, B. (1961). Letter from Barbara Chase (Paris, France) to her mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 20, 1961 (Box 1, Folder 2) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/713905qgrp-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase (Paris, France) to Her Mother, Vivian May Chase (Philadelphia, Pennsylvania) - March 20, 1961.” Letters (correspondence). Barbara Chase-Riboud Papers, 1961. Box 1, Folder 2. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/713905qgrp-cor.