One must admit that The Secret History of Wonder Woman is more of a history of the Marston family than it is a true "secret history" of the character Wonder Woman.
Originally deemed "Suprema, the Wonder Woman," which is an interesting feminine almost goddess-type name to the eventual heroine, Wonder Woman was created in the early 1940s. She is typical of a superhero because she has a secret identity. It is her secret "history" that is quite interesting. Due to Lepore uncovering lots of secret documents and papers from William Moulton Marston, we learn about Wonder Woman's "birth" through Marston's own history.
Marston went to Harvard and was avidly influenced by feminists such as Pankhurst. Marston was especially intrigued by those who were banned from speaking on campus about birth control and voting rights (and other feminist issues) all the way back in the early 1900s. Things get even more interesting when Marston and his wife (in the 1920s after both graduated) brought the niece of a noted feminist into their home. Olive Byrne was none other than the niece of the famous Margaret Sanger, "one of the most influential feminists of the twentieth century."
Here is the Marston family, maintaining a facade of the typical 1930s life, even writing in favor of the traditional family in a regular newspaper column, all the while being influenced by radical feminist ideals! Ironically, their lives were far from the norm and completely unconventional ... even in the sense that they were experimenting heavily in regards to their sex life with bondage and including others in their bedroom! Hence Wonder Woman's gold bracelets, to be ever a symbol of S & M!
Of course, on the more blase side, Wonder Woman was introduced because they needed a female superhero to entice the feminine population and earn more money. Further, critics take issue with the book because it's not really a "secret history," but more of a biography of Marston.