If you can make your interest in Harry Potter do some good, that's your business. Are you going to use your mutual interest in tarot cards and ouiji boards to do some good too? Where does a friendship based on the occult lead? You can do what you like. Who am I to interfere? Just remember how you might plan to answer Jesus at your final judgment (friendly words intended).
Keep in mind: it could be your final gasp of clean air, among other things.
Jen's a personal friend. I know for a fact she has no tarot cards and no Ouija board. And she has no friendships "based on the occult."
I suggest you'd do yourself a far greater service if you'd stop worrying so much about a fictional character and start worrying about your own judgmental attitude.
(friendly words intended)