The only plot credit I give to J.K. Rowling is the Harry vs. Voldemort as destined enemies plot. However, I'm one of those guys that believes that there's really only 10 or so plots used in fiction, they're all just told from different angles. If you look hard enough you'll probably find similar plots in Claremont's run of X-men with some trashy Harlequin romance novel. Harry being yang and Voldemort being yin isn't the first time we've seen that kind of plot. (i.e. Luke/Vader, Hal Jordan/Sinestro, Captain America/Red Skull, Mario/Wario, Daniel LaRusso/Johnny, The Jersey Shore cast/Intelligence, RPPR's Tom/Saving Throws)
Well I just did a search on whether or not there were any lawsuits due to "The Worst Witch" and found that while it doesn't appear that there was a lawsuit for "The Worst Witch" itself, J.K. Rowling has been involved in a a couple of lawsuits claiming copyright infringement of other authors' properties.
Also, this nerd librarian named James Vander Ark made some website (I found this out today) that was a lexicon of everything in the Harry Potter Universe. He then tried to make a print version of the so-called encyclopedia and was sued by J.K. Rowling, who claimed that this encyclopedia was in contention of an encyclopedia that she was planning to release. She then claimed that the "anguish" of the lawsuit sapped her creativity and she isn't going to release that encyclopedia. Eventually VanDerArk's book was released minus some protected content.
To this, Orson Scott Card, creator of the "Ender's Game" series blasted her. I love this.
"This frivolous lawsuit puts at serious risk the entire tradition of commentary on fiction. Any student writing a paper about the Harry Potter books, any scholarly treatise about it, will certainly do everything she's complaining about. Once you publish fiction, Ms. Rowling, anybody is free to write about it, to comment on it, and to quote liberally from it, as long as the source is cited.... She let herself be talked into being outraged over a perfectly normal publishing activity, one that she had actually made use of herself during its web incarnation. Now she is suing somebody who has devoted years to promoting her work and making no money from his efforts -- which actually helped her make some of her bazillions of dollars. Talent does not excuse Rowling's ingratitude, her vanity, her greed, her bullying of the little guy, and her pathetic claims of emotional distress."
I'm going back to sleep now