It's definitely a difficult situation. Things in life are often not applied in simple, well-comprehended answers. However, here's my viewpoint:
If it was me that had that kind of friendship before, I'd definitely NOT terminate the friendship. Why you ask? It really all depends. The main logical (and Biblical) reason to not hang around with "bad" people is so that they do not influence you for the worse (
Psalms 1 talks about this). However, I do not think the Bible is telling us to abandon every non-Christian and live like a hermit.
I would say that this is probably the will of God. He wants to use this friendship so that you can witness to her with your words and your actions. Here's a good example: While you're catching up mention how you became a Christian.
Something to remember: Don't ever consent to do anything sinful.
People in the Wiccan and people who are in the occult are no different from anyone else who doesn't know Christ. As the saying goes, "If you're not one of us, you're one of them". This entire situation isn't dealt with different if she's a Wiccan or anything else (although you'd probably approach it differently for some situations).
Don't let her influence you. You have been put in a very special position to witness. If you are not interested in finding ways to witness, the obvious answer is to get rid of the friendship.
Take it one step at a time, remember to pray and get others to pray for you, and just trust God. If it is God's will for you to witness to her, you don't have to worry about your own personal faults. God can use you no matter what as long as you're open.
We'll pray for you!