As a Pagan, I have met Pagans that wanted to take over the world - but not on a religious level. They wanted to make the world a more peaceful place by pushing acceptence and tolerance. (Note: Tolerance does not mean agreeing with something, it means putting up with something - big difference) I will say (again) that I down Rowling has any plans of world domination.
Everyone believes that their feelings on a given topic are correct. When it comes to something such as belief, we all feel that we are looking at it "correctly" and even people that have similar beliefs are prone to disagreement on various points. It is natural to want to express your opinion, and it's natural to disagree with differing opinions. In context, if Rowling *does* feel that she's the head of some religious movement, it's only natural - nearly every faiths followers follow the same pattern - including my own. I think primarily it's just a matter of degrees
BTW, if you want clarification on anything that I've said above, just ask - I'm a little spacy tonight from a lack of sleep so my coherance may not be up to snuff