I haven't read her diary entry, but, I think that the LC should be held liable to an extent for allowing something like that on the site. Foreknowledge could damage sales of the books. (not that she would miss the money!)
JK Rowling said:Some, perhaps, will read this and take the view that all publicity is good publicity, that spoilers are part of hype, and that I am trying to protect sales rather than my readership. However, spoilers won't stop people buying the book, they never have - all it will do is diminish their pleasure in the book.
JKR's website said:Even if the biggest secret gets out - even if somebody discovers the Giant Squid is actually the world's largest Animagus, which rises from the lake at the eleventh hour, transforms into Godric Gryffindor and... well, I wouldn't like to spoil it.