The three star review seems to indicate that part of the book is fiction and part isn't. I'm not sure, though, without having read it...
I think the person who wrote that review didn't catch that it is narrative nonfiction and/or misunderstood what it is. I haven't read the book--obviously--but I read the sections available for preview and didn't find anything fictional.
I also wonder why the reader is disturbed by the author trying to understand Franziska Schanzkowsky's thought process. In most cases, a historical person's thoughts and motives are not laid out and need to be parsed out from what is available. I'm not dismissing her/his criticisms, just wondering....
Some people think that by trying to understand her thought process their making excesses for her actions and to an extent making her sympathetic. It's like the reaction people have about studying Hitler as anything but a monster. I'm obviously not comparing Hitler and Anna Anderson but you get the point.
To many she was a woman who thoughtlessly took the idenity of a young girl who was savagely and brutally murdered and paraded around like she owned the name, benefited greatly from it, and didn't care who she hurt in the process (Anastasia's family/friends). She's a cruel, selfish, nasty person who doesn't deserve to be understood even on the smallest level because they feel as if she danced on Anastasia's grave cheapened her memory (there are threads on the forum that discuss the topic). Anastasia and the fraud, Anna Anderson, go hand and hand in the minds of millions and that leaves a bitter taste. To them she doesn't deserved to be studied, but forgotten and buried never to be mentioned again.
I'm not saying I feel the same way but I understand why others think negatively about it.