As an adult, her anorexia conquered, Liu became more and more fascinated by the grandmother she never knew, who taught English in the US and fell in love with an erudite and revolutionary Chinese student in her care. When he saved her life in the earthquake of 1906, they eloped to Wyoming - the only state in the American West where inter-racial marriage was legal.
Five years later, after racist threats and prejudice in California, where it was a crime for people of different races to touch in public, Liu's grandmother, Jennie, and grandfather went to China. There they spent the nearly 30 years.
He worked as a political activist while she raised four children, endured yet more racial prejudice, this time from the Chinese, and survived major historical events such as Chiang Kai Shek's White Terror massacre in 1927 and the Japanese attack on Shanghai in 1932. Jennie finally gave up and returned to California with her children in 1935. She never saw her husband again.
Liu knew very little about her father's childhood in Shanghai, but after a trip to China with her parent in 1979, and visits to some of her father's childhood homes, she began teasing information out of him which she recorded in notebooks. There were some photos and a letter from her grandfather 15 years after her grandmother had left him, asking her to take him back. Jennie's eldest daughter, Blossom, had also began a memoir of her childhood in China, which helped Liu with details. But the gaps were so big that Liu decided to fictionalise her grandmother's story.
The result is Cloud Mountain published here this week - a hugely entertaining, epic sweep through Chinese history and one very passionate love affair. The book has been sold to 12 countries, including China, since it was published in America last year. "I was jealous of my grandparents," says Liu, "for having had such an adventurous life. I wanted to get inside their heads and see what it must have felt like, for example, on their midnight escape from Peking, which my father remembers."
Liu clearly relishes and romanticises her family's exotic past. Her eyes light up when she tells me how clever her grandfather must have been, speaking seven languages, including Latin. She is small and pretty, wears a waistcoat decorated with Chinese characters and bears an uncanny resemblance to her grandmother in one of the enlarged, mounted photographs that she is keen to show me. She has used tried-and-tested fictional devices to make her grandmother seem even braver, by portraying her as an admirable, Louise Bryant-type figure, who wrote articles for the American press and sent photographs of the Chinese poor with her dispatches.
Liu even attributes her anorexia in part to the culture clash of her parents' marriage, which in some ways echoes that of her grandparents. "My brother left to get married when I was 14 and my parents fought each other through me. I was split, with a love/hate relationship with my mother, who was this voluptuous American stereotype, and this affection for my father which I couldn't express. In some ways, I was making myself into a Chinese doll to please him."
Cloud Mountain is a Chinese Reds or Doctor Zhivago rather than another Wild Swans - riveting, romantic and readable. But it was Liu's sensitive understanding of the psychological ramifications of inter-racial relationships at that time that is most captivating and poignant. After 30 years of a passionate relationship, in which they had six children, four of whom survived, neither grandparent was able to shed their cultural heritage.
"In addition to the crossing of cultural worlds it was an interesting period, as Western concepts of romantic love were changing with people like my grandmother wanting more of a partnership," Liu says. "My grandfather was also flipping between the old-style Chinese view of marriage and the more western attitude he so admired." Their passion must have been great to withstand racial prejudice. Liu says that much of the prejudice was class-based; the lower the class the more inter-racial marriages there were.
"A great many American-Irish women married Chinese men. They were barmaids and laundry girls and they were quite a perky group. There are pictures of them decked out in Chinese stuff. On the east coast it was frowned upon but not illegal, but on the west coast it was very much more threatening. Some periods were much worse than others. It was very bad in the 1870s and a lot of Chinese were killed. By the 1920s it had started to lighten. By World War Two, anti-Japanese sentiment overlapped and the Chinese would wear badges saying, "I'm not Japanese". But they were still Asian.
Liu now lives in Los Angeles with her husband, who is of Russian-Jewish descent. "It seems as if everyone in my son's school has inter-racial parents and it's a wonderful place for a child of mixed blood. But parts of the US are still very hostile, particularly in the rural South. If you go just 40 or 50 miles inland from LA to Riverside, the atmosphere is entirely different. I've heard of people who are drummed out of town with telephone threats and comments on the street. It's more of a black and white issue now, but the anti-Asian sentiment is still strong. There have been several cases recently of Asians killed in racially motivated murders."
After an extraordinary childhood in China, Jennie's children had to get used to America. Blossom, the eldest married a "military creep who forbade her to tell anyone she was Chinese" and died in penury in a trailer in Arizona. Loti was a very beautiful Eurasian starlet who played the sing- song girl in the film The Good Earth and married successive rich men. Herb, the "baby" had to join the army in the Second World War to become a US citizen and not be deported to China and spent five months in a German POW camp.
But it is Liu's father, Maurice, the eldest son, who has carried the Chinese torch of his ancestry. "He has got far more Chinese in his attitudes as he has got older. He is very passive-aggressive, which is a typical male Chinese character trait - trying to control and supervise everything without lifting a finger."
These are exceptional stories in their own right. "I'd love to write them up" says Liu, " but that book will have to wait until everyone's dead."
Cloud Mountain, by Aimee Liu, Headline, pounds 16.99.