MLA

Luhan, Mabel Dodge, 1879-1962. Lawrence, Frieda von Richthofen. Box 65, folder 1762. [1938?], n.d.. https://collections.library.yale.edu/catalog/2002407.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 65, folder 1762"])([1938?], n.d.)[Lawrence, Frieda von Richthofen]. https://collections.library.yale.edu/catalog/2002407.