It's not about the money. It is all about control. She doesn't care if Mugglenet makes six-digit profits, that "What will happen in HP7?" became NYT's #2 bestseller, or that The Leaky Cauldron's admin bought an apartment in New York with the money that the site made. But she cares that someone would take attention from HER encyclopedia.
I understand the desire to have one's world in one's hands, as it were, but my sympathy is on RDR's side, because they're not publishing _fiction_ about Harry Potter - they are publishing commentary. And as to her reaction - what Jason said.
(As to her encyclopedia, maybe it's for the best if she does not publish it. A book which tells us who marries who, who has how many children and who sleeps with what gender? Sorry, not interested.)
An interesting question, by the way: what if we published a commentary on Salvatore's books? Or an encyclopedia on Faerun? Where would we stand then, in terms of copyright infringement?