Which of the following individuals was not mentioned as a significant contributor to Delta Sigma Theta's organizational structure?

The correct choice refers to Margaret Johnson, who is not recognized as a significant contributor to the organizational structure of Delta Sigma Theta Sorority, Inc.

The sorority's foundation was influenced by several key figures whose contributions laid the groundwork for its establishment and growth. Individuals like Gladys Byram Sheppard, known for her leadership and commitment to the sorority's mission, Ethel Lamay Calimese, who played an important role in its early years, and Anna Johnson Julian, who was instrumental in the sorority's initiatives and policies, are documented as pivotal in shaping its organizational framework and history.

Margaret Johnson, while potentially a member or associated with the organization, does not hold the same recognized stature or contributions in the context of Delta Sigma Theta's foundational contributors, which is why this option stands out as the correct answer.