Socialite, Heiress, Her grandfather ran a railroad, and her father was an ambassador, a governor and a cabinet secretary. She married the grandson of an oil baron at her family's 25,000-acre estate. She was a first-rate skier and equestrienne, riding magnificent cavalry horses that were a gift from Stalin. She knew well the whirl of dances, luncheons and teas that were traditional for women of her time and station. And yet ... Her marriage, in 1947, took place when she was nearly 30, an unconventional choice for any woman of the era. Before that, she had worked as a journalist and had witnessed the aftermath of one of the most notorious massacres of World War II. Kathleen Harriman Mortimer, a daughter of W. Averell Harriman, died on Thursday at 93. The death, at her cottage in Arden, N.Y., was confirmed by her son David Mortimer. Mrs. Mortimer also had a home on the Upper East Side of Manhattan. Though she was a far less visible public presence than her father — a United States ambassador to Moscow and London, a governor of New York and a secretary of commerce under President Harry S. Truman — Mrs. Mortimer was quietly accomplished throughout her life and, when she could be, graciously subversive. Mrs. Mortimer's life is a window onto both Gilded Age America and the changing role of American women in the era between the world wars. For her life — which encompassed extraordinary privilege, spirited adventure, associations with the most prominent actors on the world stage and also a measure of heartache — stood squarely at the nexus between 19th-century old money and the 20th-century New Woman. Kathleen Lanier Harriman was born on Dec. 7, 1917, the younger of two daughters of Mr. Harriman and his first wife, Kitty Lanier Lawrance. Her paternal grandfather, E. H. Harriman, head of the Union Pacific Railroad, had left a fortune estimated at $70 million to $100 million. Her parents divorced in 1929. Kathy, as she was known, grew up at Arden House, a 40-bedroom, neo-Renaissance house high in the Ramapo Mountains. (For guests who quailed at the climb, it could be reached by funicular; when a horse was required, it glided up by funicular, too.) Miss Harriman earned a bachelor's degree in social science from Bennington College in 1940. The next year, she joined her father in London, where he oversaw the Lend-Lease Act, which provided United States aid to the European war effort. In London, she was a reporter, first for the International News Service and later for Newsweek. Her roommate there was Pamela Digby Churchill, the daughter-in-law of Prime Minister Winston Churchill. As befits a tightly knit society in which people were separated by far fewer than six degrees, Pamela Churchill would, years later, become Averell Harriman's third wife. In 1943, Mr. Harriman was named the United States ambassador to Moscow, and Miss Harriman joined him there. She learned Russian; was the official hostess at her father's diplomatic functions; and traveled with him in 1945 to the Yalta conference, at which President Franklin D. Roosevelt, Churchill and Stalin hammered out Europe's postwar reorganization. (On their return to the United States after the war, Stalin gave Kathleen and her father two of his finest horses as a going-away present.) Miss Harriman's Moscow exploits were widely covered by the American press. "With the possible exception of Eleanor Roosevelt and Deanna Durbin," The New York Herald Tribune wrote in 1945, "Kathleen Harriman is the best-known American woman in the Soviet Union." Her time there included a far darker obligation. In 1944, as her father's representative, she accompanied more than a dozen foreign correspondents into the Katyn forest, in western Russia. The forest had been the site of the massacre of thousands of Polish officers earlier in the war. Now the journalists had been taken there to witness autopsies of the exhumed bodies, part of a Russian disinformation campaign to ensure that Germany would be blamed for the killings. Aided by many unwitting news organizations, the myth that the Nazis had carried out the killings endured for years. In fact, the massacre had been perpetrated by the Russians, something that was admitted only decades later. In 1947, Miss Harriman married Stanley Grafton Mortimer Jr., an heir to the Standard Oil fortune. Afterward, she largely dropped from public view, though her private life was not without turbulence. In 1969, Mr. Mortimer, who suffered from manic-depression, shot himself in what apparently was a suicide attempt. He survived, and the couple remained married until his death, at 86, in 1999. In 1994, as was widely reported, a group of Averell Harriman's heirs, including Mrs. Mortimer, sued Pamela Harriman and several associates, charging that they had squandered tens of millions of dollars of their inheritance through high-risk investments. Mrs. Harriman, the United States ambassador to France under President Bill Clinton, had married Mr. Harriman in 1971; Mr. Harriman died in 1986. The suit was settled in 1995; the terms of the settlement were not disclosed. Until well into old age, Mrs. Mortimer pursued her life as an outdoorswoman. She served on the boards of the Visiting Nurse Service and the Foundation for Child Development, among other organizations. All the while, her children knew little of her wartime life.