If she was, indeed, commissioned to write Razorbill's story, then wouldn't that make this a case of a fanfic author being noticed because of fanfic, but not necessarily a pull-2-publish situation?
Maybe it's a case of the fanfic response getting her noticed, and the publisher realizing that with the cleanup, she'd already written the story they wanted written, but they still wanted to retain control over the final product than if they just acquired her book.