MLA

Luhan, Mabel Dodge, 1879-1962. Wilder, Isabel. Box 38, folder 1094. 1938-51, n.d.. https://collections.library.yale.edu/catalog/32197046.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 38, folder 1094"])(1938-51, n.d.)[Wilder, Isabel]. https://collections.library.yale.edu/catalog/32197046.