I'm not entirely sure what the work in question is about... is it just a compilation of different facts derived from Harry Potter books? If so, then this case could be quite a challenge to determine if it is "fair use" or not. On the one hand, all the information in the book is derived from the books of the original author. On the otherhand, it is, itself, unique enough to bring the copyright law into question. Of course, the point was moot when there was no commercial intent involved. Honestly, from a business standpoint I think it is stupid to sue for copyright infringement. What I would do is buy the rights to the books from the librarian, package them with the Harry Potter books, and make more money. Oh well.
as always, institutional factors keep actors from a mutually beneficial transaction.