Mrs. Mellon, who with her husband preferred to live a courtly life that navigated away from the shoals of ostentation, family scandal, legal controversy, media attention and celebrity. To the extent that she otherwise embraced the world of politics, it was as a friend to Jacqueline Kennedy, who turned to her in the 1950s as a young senator’s wife in need of friendship and guidance in Washington society. Mrs. Mellon had properties in Washington, New York, Cape Cod and Antigua in the West Indies, but she lived mostly on the couple’s 4,000-acre Fauquier estate, where Paul Mellon ran his horse-breeding stable and she designed and cultivated gardens of supreme elegance. The estate, the size of Fairfax City, includes a landing strip for private aircraft. Paul Mellon died in 1999, at 91. Mrs. Mellon had a deep interest in interior design and architecture, and she became a hands-on patron of the designers she hired. But her primary interest was in gardening, landscape design and the history of gardens. Her father, Gerard, was president of the Gillette Safety Razor Co. Her mother, also named Rachel, nicknamed her “Bunny,” which stuck. “I used not to like it,” she said once, “but now I am reconciled to it.” In October 1929 — the month of the stock market crash that heralded the Great Depression — she was presented to society at a ball at her parents’ house. Three years later, she walked down the aisle with her first husband, Stacy B. Lloyd Jr., a businessman who became a noted horse breeder. Lloyd was a Princeton University graduate and a fox hunter, and as Army officers, he and Paul Mellon roomed together in London during World War II. In 1946, Paul Mellon’s first wife, Mary, died at 41 of an asthma attack. In 1948, after the Lloyds divorced, Paul Mellon married Bunny. Mrs. Mellon’s survivors include a son from her first marriage, Stacy B. Lloyd III of Washington; two stepchildren, Timothy Mellon of Saratoga, Wyo., and Catherine Mellon Conover of Washington; five grandchildren; and two great-grandchildren. A daughter from her first marriage, Eliza Lloyd Moore, died in 2008. Paul Mellon’s father, banker and Treasury Secretary Andrew W. Mellon, founded the National Gallery and funded the neoclassical West Building, which opened in 1941. When Paul and Bunny Mellon started collecting art in earnest, Mrs. Mellon introduced her husband to 19th-century French painting, including the work of the impressionists and post-impressionists. He had been more interested in British art.