Not to mention that "none" of the core characters are uniquely her own, they have all been "inspired" by others work and retooled to fit the story she created.
A witch is a witch, a wizard is a wizard, a wand is a wand, a familiar is a familiar, a broom is a broom, an elf is an elf… Should I go on?
No matter what name you characterize the "thing" with, its original concept is already preexisting. Should Wiccans be allowed to sue her for wrongly portraying "witches and wizards". They've been around a lot longer the "Harry Potter", so therefore should maintain all creative rights to the concepts created which lead to magic, witchcraft and wizardry.
Better yet, and just as ridiculous sounding. Should the Heritage Dictionary or Merriam Webster be allowed to sue her for using words and concepts that they have already defined in print?
Oh wait, those are just research"guides" created for those interested in the subject material… By folks who have compiled lists of words, phrases etc relevant to the core content.