My DD9 is going to be seeing Wicked (a surprise trip) and I wanted to get the soundtrack and the book for her to read before we go on our trip.  I can easily work in the book because her older cousins are obsessed with Wicked.  I don't think she'll put 2 and 2 together. 
My question is the appropriateness of the book on which Wicked is based.  Wicked - The Life and Times of the Wicked Witch of the West has great reviews, is worth 25 AR points, but a few of the reviews mention sexual situations in the book.  Can someone explain this to me?  This is a book that my daughter can easily read by herself but I would like to know what I'm getting into. Also, any insight or need-to-know info on the musical itself?
Thanks!