MLA
Reid, Anna. Letter from Anna Reid (Seaside, South Carolina?) to "My Dear Friends," Anna Appears to Be the Governess of the Children of Preston Brooks, Congressman from South Carolina Who Died in 1857 - November 9, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 58. https://digital.library.emory.edu/purl/160cvdndkd-cor.
APA, 6th edition
Reid, A. (1861). Letter from Anna Reid (Seaside, South Carolina?) to "My dear friends," Anna appears to be the governess of the children of Preston Brooks, congressman from South Carolina who died in 1857 - November 9, 1861 (Box 5, Folder 58) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/160cvdndkd-cor.
Chicago
Reid, Anna. “Letter from Anna Reid (Seaside, South Carolina?) to ‘My Dear Friends," Anna Appears to Be the Governess of the Children of Preston Brooks, Congressman from South Carolina Who Died in 1857 - November 9, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 5, Folder 58. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/160cvdndkd-cor.