Gladys Mills married Henry Carnegie Phipps in 1907. Her husband was the son of the wealthy Pennsylvanian Henry Phipps, the second largest shareholder in Carnegie Steel Company, after Andrew Carnegie. Gladys’s father-in-law was also an early investor in Florida real estate—at one time the Phipps family owned one-third of Palm Beach.
Gladys seemed to inherit her father Ogden’s love of horse racing. With the combined fortunes of her and her husband’s families, she devoted most of her energies to horse racing. She and her brother, Ogden Livingston Mills, purchased Wheatley Stables in 1926. They bred and raised their horses, including the racehorse Seabiscuit, at their Claiborne Farm near Paris, Kentucky. When her parents died, Gladys inherited the Staatsburgh mansion. In 1938, she gave the house and 192 acres to the State of New York. Mrs. Phipps died in 1970.