This looks like she's wearing the same necklace in this pic. Portrait of Gloria Vanderbilt by Carl Van Vechten 1958 May 23
Digital ID: (digital file from intermediary roll film copy) van 5a52734 https://hdl.loc.gov/loc.pnp/van.5a52734 Repository: Library of Congress Prints and Photographs Division Washington, D.C. 20540 USA