Well, my witchly indignation is sure as Hel rising ...
Would you guys be cracking jokes about this if the young lady were asking for copies of the Jesus book ... oh, wait, you would. Okay, so that's fair at least ...
Wicca is a religion, with a growing number of adherents. Some of them are even sensible people. I have met a few. It is one of a variety of pagan paths that are gaining (some say regaining) popularity.
What the girls on Charmed are doing isn't Wicca. Neither was The Craft, although both lifted convenient and theatric looking elements from the religion.
Spells are prayers ... so there isn't much differnce between praying to God that so-and-so notice me and take me to the dance and going through a lot more dance steps to make the same request of multiple Gods/Goddesses. What's important is that your daughter learn that this is a religious path, rather than a source of power and control.
Most reputable teachers will not take a student under the age of 18 ... that's a long-established tradition, mostly to avoid any freaking out parental issues ... or in some cases charges of statutory rape.
There are sexualized elements of the religion, and there are some unscrupulous bastards (and bitches) out there that use sex as a means of power and control.
There is a lot of information available on line, much of it repetitious ... so are many of the books available, incidentally. Everyone has their favorites. I usually suggest two of Scott Cunningham's books ...
Wicca: A Guide for the Solitary Practitioner and
The Truth About Witchcraft Today. The second book I think would be particularly useful for you to read.
Kids being kids, the more you restrict her from learning about something, the more interesting it might become to her.