What do most career women do after a successful run on Madison Avenue? Catherine Finerty watched her friends settle into the country-club life. She opted instead for Mexico.

When the 60-year-old widow loaded up her car and headed south, what she found at the end of the road was far from what she expected. Finerty settled into a comfortable house just outside of Guadalajara and, although not a Catholic, she soon immersed herself in Franciscan volunteer work. It wasn't long before she found herself visiting small settlements hidden in the tropical mountains of western Mexico,...