Well 1) I believe Chritianity is the best religion, Although I respect all religions.
2) If your mother truly is Christian she won't disown you infact she'll love you the same or more
3) When one is considering a religion, your considering changing who you are, who you'll be, and who you want to be. This is a huge decision I'd do whatever you want to do, but think about it very much. I'd pray about it, but I'm Christian, and you are thinking about becoming Wicka so I don't know what you'll do unless you still have a faith in God.