Patty,
The little booklet
From Girl to Woman is a very short, very to-the-point booklet that is very inexpensive and could easily be read in one sitting. It does not go into consummation in marriage, making it a great first step into understanding puberty in a God-honoring way. I would encourage you to just go ahead and get that one little booklet and go over that with your little honey now. The rest of the
Beautiful Girlhood study is not as much about the changing body as it is about how to live for the Lord as girls grow into young womanhood.
If you do go the route of going over the little booklet now, I would encourage you not to talk too deeply beyond what is in the booklet, but simply be open to allow your daughter to ask questions. Often, young girls don't need all the answers at such a young age, and if you're anything like me I tend to overtalk something! Young girls often just need an understanding that God has planned for their body to change in this way.

Another thought would be to just get the Girl Option Package to peruse the books yourself. Then, if you felt your daughter needed what they contained now, you could decide whether to add the RTR guide for that or not then.
Here's a link to the booklet description:
http://www.heartofdakota.com/rtr_hearts ... girl-woman
It can be purchased for $3.95 off this link:
http://www.heartofdakota.com/rtr_hearts ... ckages.php
(You'll have to scroll down a ways to find it.)
Hope that helps! Honestly, the booklet is the easiest way to introduce puberty that I've found! My older sister, who has 7 children, agrees
From Girl to Woman and
From Boy to Man are the best things she has ever used for that stage too! I recommended both to her when her oldest children first hit puberty, and she was so relieved to get the booklets in hand and be able to immediately address puberty in such a Biblical way.
Blessings,
Carrie