This is neither casta diva nor cast a diva, this is more like άστα ντίβα. I was expecting something like Carolyn Burke's biography about Edith Piaf and instead, I got this... Do you know those cheaply made, rushed, gossipy, one-sided, unauthorised biographies about the British royals? Something like that... but worse.
A portion of the material used, according to the author, comes from archives, with unpublished papers, she specifically mentions (in a youtube interview) the Stanford archives where she found 30 years of correspondence between Callas and her Godfather, copies of medical certificates etc. She also mentions letters, written in Greek between Callas and her mother - which had to get them translated because she understands no Greek (neither language... nor culture if I may say so) - and other people (husband, colleagues etc). Besides that, which adds little or no actual new information, there is just some basic, select bibliography, bits and bobs from magazines... the bare minimum of research, really.
I wanted to learn more about Callas' work, about her singing, I was looking for a more thorough analysis of her major performances, but instead, I mainly got repetitive, behind the scenes, petty dramas. To be honest, I couldn't find any information about the author's level of music education but, if any, it definitely does not shine through her writings.
I also found quite condescending the way the author handles some historical events about the Greek civil war, a very sensitive subject, and she obviously has a superficial knowledge about Greek history, so... Why?
Anyhow, I encourage you to check this book, read a sample or borrow it from a library and if you find it suitable to your taste, sure, go ahead and buy it. But for me, it was a huge disappointment and I regret wasting my time.