"Hookups" encompasses activity other than sexual intercourse. This book would likely help its readers negotiate how to engage in that activity safely and with consent. And 13-year-olds hook up with each other, as do kids 14 and older, which your daughter will in all likelihood become.
Again, if you had bothered to actually read the book, rather than make a snap judgment based on a one-sentence summary on the internet, you'd probably be better informed.
Fwiw, I think psychologists would say it's healthier than stigmatizing sex and pretending it's a concept that pops into existence once people turn 16 or 18. (Ironically, some people are molested way before that age and don't even understand what's happening and why it's bad -- probably because they had no educational resources on the subject thanks to attitudes like yours.)
The average age of first sexual intercourse in the US is ~17 for both boys and girls, and rising. The hypersexuality of adolescents is overstated in popular media, though probably varies by region. I grew up in a pretty promiscuous environment, and even there, while there were 13-year-olds having sex, and we were aware of it, that was by far the minority experience.
And minority experiences are not allowed? How would that be any different from "5% of the population is gay, so we're just not going to allow that to be talked about"?
And FWIW, the age of consent in the U.S. is 16+.
13...my goodness man...