The author says that this is a biography. While it may have been steeped in biographical research, this is, in fact, historical fiction. The book is novelistic in style and is filled with conversation that was made up because the author wanted to help the narrative flow of the book. She admits this in her introduction.
Still, this is a good look at a woman we don't hear much about. I will have to read a more serious biography to get a better picture, but I did like what I read here.