Of course it is all just fantasy and nothing more.
Rowling spent many years coming up with the Harry Potter character and many more getting it published. Were she really in possession of some witch powers she would have written it in a month or so and gotten it published straight away.
There is a very good movie about her story that gives great insight into her beginnings.
She is not a witch nor is there anything demonic about the books or their stories. They are simply very well written fantasy stories set in a background of a fictitious world that contains elements from minor horror to outright comedy.
I really don't get the people who think there is something horrible about either the author or her works.
It was mostly started by religious zealots, mostly Christians, no big surprise there.
My personal take on them is that their faith in their religion is so fragile that they think something so benign as a children's fantasy book could crack their glass cocoon.
The fact that authors write about some subject doesn't mean that they have any further involvement. I write about murder, serial killing, torture even a bit of bestiality has popped up. But I'm not a murderer, rapist, gang member or arsonist and I certainly don't practice any form of bestiality, nor do I promote or admire any such things.
Rowling's works simply contain all the story traits that make good books and movies, as do the works of most successful authors.
Speculation that she is a witch or that her books are going to convert children into practicing witchcraft are just plain silly.