To avoid a repeat of this discussion, this isn't a libel thing, it's an online harassment thing (https://www.service-public.fr/particuliers/vosdroits/F32239?lang=en) and a complaint, not a lawsuit. So contrary to popular belief, there isn't any burden of proof on anyone here because it doesn't matter what the truth is for this type of thing.
I don't think they can do that. The punishment would be a fine on Rowling but I don't know if they have jurisdiction. I expect nothing to come of this.