I'm not that interested in reading the book but I would quite like to read her contemporaneous diary entries - these are important prime sources and we would be free to make our own interpretations taking into account the work done by other people (e.g. Bill Griggs).
Are these diary entries reproduced verbatim in the book? If so, the book is important to Holly addicts. If not, it's just another chronicle of events, albeit from someone who was there, but embellished many years after with all the risks that entails.