"I don't know how much research she did, but there's no question that she did quite a lot," Elizabeth Kronzek says. "I think she's been interested in this stuff all her life and is probably somebody who was reading folklore and mythology from a young age. "As I was reading the books, I thought certain names were so funny: grindylows (water demons), hinkypunks (one-legged spirits) and red caps (evil goblins). I was sure she'd made them up. But I discovered that, no, these are actually from European folklore. Some of them are from very, very obscure folklore."
As quoted in a USA Today article and posted on FR Here
Read the fourth and eighth paragraphs. I suppose you could try to draw a distinction between "very obscure folklore" and "occult materials"; but I consider it a false distinction, in that what is folklore to you or me is someone that a Wiccan or neo-Druid will actually take seriously.
See also, later in the article:
"I don't think she got anything wrong in all four books," says Allan Kronzek.
Rowling, a former French teacher and single mom, has been quoted telling a curious fan: "Go and look it up. A little investigation is good for a person."
All in good fun, right?
Yeah, and there were "witches" in England complaining that the kid's in the quidditch match in the movie were riding their brooms backwards.
I would note with our sources that, while yours is what someone thinks Rowling was doing, mine is a direct quote from the author.
And for the record, a little research never hurt anyone.