As her modeling career came to an end, no one was knocking on Kathy Ireland’s door asking her to endorse—anything. Everyone expected the Southern California native to put her efforts into swimsuits. It was the obvious choice for a woman who graced the cover of Sports Illustrated three times and made thirteen appearances inside the magazine. But “obvious” never was Ireland’s style.

Before she was a supermodel, Ireland was a businesswoman. At age four, she designed and sold painted rocks from her wagon. She charged a nickel. Her sister charged ten cents. She was already under-promising and over-delivering...