You asked what the real Madame Mao was like and how she looked. I imagine she was stunning in her 20s, when she showed up as an aspiring revolutionary in the caves of Yenan. (Even if she weren't, she would have seemed pretty hot to Mao and his colleagues: She had come there from cosmopolitan Shanghai, they had come from the Long March.) Certainly she didn't age like Lauren Bacall or Katherine Hepburn; the pictures of Jiang Qing in 1972, entertaining the Nixons at a revolutionary opera, show a plain, austere face without even a trace of animation, much less humor.
What interests me about her is not really in this book. It's roughly related to the question you ask: Did she have any appeal, besides her (seeming) relationship to Mao and the fear that inspired in others? In the quarter-century after Mao and the Communists came to power in 1949, the underlying and divisive question was, what was the source of their revolutionary power: Was it the Communist Party as an organization, or Mao personally? Deng Xiaoping, who survived the Cultural Revolution, and his superior Liu Shaoqi, who didn't, stood for the party. Mao and Jiang Qing tried to link the party to the bad parts of old China: the bureaucracy, the Mandarins. But in turn, Mao and Jiang Qing could be tarred as a vestige of old China, too: the emperor and his court.
The real Madame Mao seemed to love luxury, at least in her later years. That aspect isn't in the book, but there is plenty of evidence of this. At the height of her power, during the austerity of the Cultural Revolution, she watched movies in her private screening room that the rest of the country couldn't see, had access to private estates, lived high. (I once wondered if these signs of her monumental hypocrisy were just a smear propaganda campaign: After all, some of the stories date back to her show trial, when her mortal enemy Deng Xiaoping was building the case to jail her for life. But in China, I heard the stories firsthand: I met a musician who wasn't sent to the countryside in the Cultural Revolution because he played in a private orchestra for Jiang Qing, letting her hear the classical music that was banned throughout China.)
In a sense, Becoming Madame Mao is the first, though failed, attempt at a new genre in literature about China. There really isn't any historical fiction about high-level politics in the modern era. To be sure, there is good fiction about the life of ordinary people: Ha Jin's Waiting deserves its awards. There are great memoirs: Jung Chang's Wild Swans, Nien Cheng's Life and Death in Shanghai. There are great collections of essays: Simon Leys' Chinese Shadows. My own favorites are histories: Barbara Tuchman's Stilwell and the American Experience in China and one of Jonathan Spence's lesser-known books, To Change China. Spence's short new biography of Mao is also OK. (On the subject of journalists' books, well, as a judge might say, I'll recuse myself.)
But historical fiction? About people currently or recently in power? Chinese writers inside China couldn't do it, for obvious political reasons. Not that someone inside China couldn't trash Jiang Qing: She's been officially in disgrace for 24 years. But how would the novelist depict Mao? What if he or she wanted to describe Deng Xiaoping in a way akin to Henry Kissinger's initial (later regretted) impression: "that nasty little man"? Suppose someone in China tried to write fiction about something slightly more distant, like Chiang Kai-shek and Madame Chiang: Could the writer humanize them, or portray them as less than unalloyed evil? Remember, this is a country where even very ancient history, the stories of hundreds or thousands of years ago, is dredged up to convey oblique metaphorical messages about the present (as Min describes on Page 218, the use of the play Hairui Dismissed From Office at the beginning of the Cultural Revolution). So I don't think from inside China we're going to see any great historical fiction about modern leaders.
Outside China, there hasn't been much in this genre, either. American and other China specialists write histories; novelists (with the noteworthy exception of Andre Malraux) have been too intimidated to take on a subject like China. So it's only now, as Chinese like Min have begun to leave the country and to write about it from outside China, that we have the chance to get this sort of historical novel.
It's unfortunate that she ended up with such a thin, Americanized view of Jiang Qing, but I guess the effort, by itself, represents a kind of progress for historical fiction about modern China.