[4] She had a twin sister, Beatrice, Countess Granard (1883–1972),[5] and a brother, Ogden Livingston Mills (1884–1937) who served as the United States Secretary of the Treasury.

[6] Mills Phipps was an avid ice skater and an excellent golfer; she won a number of tournaments, including a match play championship at the Newport, Rhode Island, golf course in which she beat her male counterparts.

Phipps was said to be most happy during her morning hours at the racetrack, where she would watch her horses exercise, accompanied by two pet poodles.

[9] Throughout her time as an owner, she bred, or co-bred 102 stakes winners, including Bold Ruler.

[2][1] Following her brother's death in 1937, Gladys Mills Phipps inherited their parents' mansion at Staatsburg, New York.