This is a devotional for Christian teen girls with 101 devotions covering faith, Christian life as well as people and life skills.
People and life skills chapters I liked very much (I would even add more chapters on practical life and striving to be a woman of grace).
As for the "mean girls" - there are few chapters about the subject, but I would add more (maybe about mean guys, too).
As for the Christian content - unfortunately, I find these chapters being quite didactical, I would use more storytelling and the examples from the lives of real Christians. Teenagers pose many questions and I think that there was not enough space for discussion as a way to engage them in authentic Christian beliefs.
Also, in my opinion this is written as a devotional book for practising Christian girls from good environments/families - I would appreciate more chapters open to girls who are questing/entering the faithful life or experiencing the difficult realities of life (i.e toxic relationships; drinking; chastity as a way of life and sexual life; honesty, lying and manipulation etc.).

Some great advice for teens. Honestly, I skimmed it, but it seemed well written with a bit of humor to make it readable.