Almost invisibly in her own day, Natalie de Blois, of SOM, helped guide the design of three of the most important corporate landmarks of the 1950s and 60s — the headquarters of Lever Brothers, Pepsi-Cola and Union Carbide — whose suave steel-and-glass facades still exude the cool confidence of postwar Park Avenue. “There wasn’t anybody in the country quite like Natalie, because there was no one else working for a firm quite like Skidmore,” said Beverly Willis, the founder and chairwoman of the Beverly Willis Architecture Foundation in New York, which seeks to raise the general consciousness about the role of women in the building industry. “At that point, there were only five or six women across the U.S. who had a substantial architectural practice,” Ms. Willis said. “And, of course, Natalie was doing bigger buildings, and she was doing them in the heart of Manhattan.”