If it is completely fantasy, and is not tied in at all with the true practice of witchcraft, WHY did she do this?
For instance, Slytherin may sound like a harmless pun; but it is actually an actual demon that is called upon in Satanic practices.
Secondly, you need only look at the correlation between one topic and another to see if it is a good thing or a bad thing. Go ahead, do a web search on google.com with search terms like "slytherin witchcraft -hogwarts" (use -hogwarts to eliminate the many uses of this term in kids' pages); it ain't exactly kiddie stuff.
If in the course of writing a novel, I do research into Christianity and include some of its arcana in my book, does that make me a Christian or one who is tied in to the true practice of Christianity? Does this also work for Jewishness? the Masons? the Illuminati? the Klan? the Knights of the Round Table?
Then, I'm going to run it through the "Disgronificator."
If I hear Slim Whitman singing "Uma Paloma Blanca," I'll have to admit that the Holy Rollers here were right.
But, until I do...