The Americans included about a dozen OSS personnel and about 18 U.S. airmen.
Liu "was not comfortable with the Russians," he said, and when the Americans asked her to join them as an interpreter and guide, "she eagerly accepted."
The OSS group, he said, "had to find food and a way out, so they had to have someone who could talk to the villagers to get intelligence and also buy food."
Posing as a peasant girl, Liu had several confrontations with German soldiers on roads and in villages, said Downs. But, he said, "she got by through wit and guile and her German [language] ability."
Liu and the others not only had to deal with the enemy but with the weather.
When a blizzard hit Mt. Dumbier, Liu recalled in Downs' book, "the wind blew so hard that it turned people over. Our eyebrows and hair changed into bunches of icicles."
They didn't dare sit down, even for a moment, she recalled. "We later saw those partisans who tried it -- and froze stiff. We later counted 83 of them."
On Dec. 26, most of the Americans were captured in a hunter's hut during a surprise raid by the German intelligence unit.
Liu, however, was in another area and avoided capture.
From then on, Downs said, it took Liu and the four agents who were with her -- two Americans and two British -- nine weeks to get to the Russian lines in Romania.
"That was a tricky operation because there were Germans everywhere," said Downs. "They were shooting people on sight."
After reaching Bucharest, Romania, on March 1, Liu was flown to OSS headquarters in Italy, where "she was put on Army status so she could get paid," said Downs.
She later was sent to Prague as an interpreter and met Allen Dulles, who had been OSS chief in Switzerland and later became director of the Central Intelligence Agency.
With the help of Dulles and OSS head Maj. Gen. William Donovan, Liu immigrated to the United States with a scholarship to Vassar College after the war.
At an awards ceremony at the U.S. Military Academy at West Point in 1946, Donovan personally awarded the Bronze Star to Liu for her service.
"All I knew, I wanted to help those guys in any way I could," Liu told the Ventura County Star in 2004. "I believe in freedom."
Liu, who became a U.S. citizen in 1952, worked for many years as a real estate agent.
She is survived by her husband, Hans P. Liu; her son and daughter from a previous marriage, Edmund Peck and Lynn S. Peck; her sisters, Ana Gulovich, Tanya Kalenska and Eva Lamacova; and a granddaughter.