MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Standing next to "Zwei Welten" at Yale University Art Gallery exhibition; Standing in middle of exhibition at Yale University Art Gallery. Box 70, folder 1803. undated. https://collections.library.yale.edu/catalog/2014476.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 70, folder 1803"])(undated)[Standing next to "Zwei Welten" at Yale University Art Gallery exhibition; Standing in middle of exhibition at Yale University Art Gallery]. https://collections.library.yale.edu/catalog/2014476.