Girling Up; How to be Strong, Smart, and Spectacular by Mayim Bialik

I read this one in anticipation of having my daughter read it as she matures. It was wonderful for that purpose! Bialik focuses on what is happening to your body, your emotions, and your life in general as a girl matures. It's written in a way that can be easily understood and leaves nothing out. 

I would recommend this one for preteen girls, for sure.