I can see everything closer to the perspective of a teenager, but can't be sure these work. I'll give it a try though:
I think you could start with explaining Paganism. Talk to her about the wheel of the year, the pagan holidays, their meaning, the gods and the way they can help.
Then, the phases of the moon. Thanks to all the teenage TV-series that involve vampires and werewolves, she will be fascinated by the power of the moon.
While talking about all this, involve the term wicca and only a few info about it.
Then introduce her to Wicca. After that, explaining magic and energy work in a very simplistic and modern way, should do the job. She will have to be able to talk about all these at school and with her friends. If she is very social, witchcraft and Paganism have to be possible to explain to the less open-minded children, without making her seem a weirdo in front of the others.
Good luck, and let us know what your little witch thinks
"The strength of the pack is the wolf, and the strength of the wolf is the pack" - Rudyard Kippling ⛤