I'm not Wiccan, being a Satanist -- and modern Satanism is really more of a philosophy than an actual religion.
But I can recommend a couple of books on Wicca which I think your friend may enjoy and which her mother may not even find too objectionable.
The first is *The Sprial Dance* by Starhawk. This book has been revised to be more inclusive of men than it was when it was first published, and it still remains one of the essential handbooks to have emerged from the Wiccan movement of 1960s and '70s.
http://www.amazon.com/exec/obidos/ASIN/0062516329/qid=1008522373/sr=1-1/ref=sr_1_2_1/002-3345803-5364004
The second is a *beautifully* bound little book I picked up not too long ago, titled *Simple Wicca* by Michele Morgan. This book not only clearly presents the basics, but also defines the differences between the various "traditions" (or, styles) of Wicca, which can be confusing to the uninitiated. It may help your friend to decide which of these traditions she'll want to further explore.
http://www.amazon.com/exec/obidos/ASIN/1573241997/qid%3D1008523025/ref%3Dsr%5F11%5F0%5F1/002-3345803-5364004
Either book makes a lovely Solstice gift. :)
-- Nanaea