This book owes much to Jennifer Homans', "Apollo's Angels," which is a significantly more exhaustive and broad-ranging history of ballet, that occasionally references the ballerina/concubine occupational conflation that has occurred throughout history. Deirdre Kelley doesn't hide the fact that she owes a measure of tribute to Homans' book; she periodically quotes from it.
Kelley's intent with this book seems to be the expansion of the tantalizing tidbits that Homans leaves when referring to the ballerina/concubine culture, at least initially. The first half of Kelley's book reads, at best, like "Apollo's Angels" light, and at worst, if one wants to think of it that way, like a tabloid gossip column.
The second half of the book, however, reads quite differently. Kelley unleashes an oddly venomous and vitriolic sequence of chapters attacking modern day ballet company life. Did you know that George Balanchine is solely responsible for the outbreak of anorexia and bulimia among ballerinas? According to Kelley, he is. In addition to sharing her anger at Balanchine, and Balanchine as Artistic Director almost exclusively, Kelley devotes a tremendous volume of words addressing ballet company labor relations in Canada and the USA. Truth is, ballet company life is generally awful in the USA and Kelley takes time to point that out. (Time and again second-tier ballet companies harvest young dancers from their summer programs as "trainees" to fill out the corps and often pay them nothing for the privilege. Then, after a year or two they dismiss the young unpaid ballerinas and find a new crop of slave labor from their summer program.)
If you are seeking a more thorough historical read, I recommend Homans' book. This book is an interesting read, depending on which half of the book appeals to your taste more.