Well, she had a good run, but you can't run from the Warner Bros secret police forever. Since the passing of the 2000 Act of Parliament stating that every British-born member of Equity, the UK actor's union, had, by law, to appear in at least one Harry Potter film whether they wanted to or not, the rebels and stragglers put up a good fight. Some moved to the States to avoid the draft, others took a heavily disguised role to keep their identity secret (Chiwetel Ejiofor's performance as Ginny Weasley will never truly get the credit it deserves).
But the final hold-out has been tracked down -- Scottish actress Kelly Macdonald, star of "Trainspotting," "No Country For Old Men" and, most recently, HBO's "Boardwalk Empire," on which she's been a revelation. Macdonald revealed to Vanity Fair (via Collider) that she's finally going to crop up in the octology in the final film, "Harry Potter and the Deathly Hallows Part Two," as the Ravenclaw house ghost.
Wikipedia tells us that the role is that of Helena Ravenclaw, the daughter of house founder Rowena Ravenclaw, who stole a magical item from her mother (an item that proves to be vital to the plot), only to be murdered by the Bloody Baron. The role was previously taken by Australian actress Nina Young in the first film, "Harry Potter and the Philosopher's Stone."
It's not exactly going to be an enormous role (and presumably the effects involved are why the casting has being revealed late), but it's another addition to the master list for our spot-the-character-actor drinking game. Macdonald will next be seen alongside David Tennant and Alice Eve in the romantic comedy "The Decoy Bride," as well as the second season of "Boardwalk Empire," while "Harry Potter and the Deathly Hallows Part Two" hits theaters on July 15th, 2011, when we'll hopefully be treated to another 45 minutes of the characters arguing in a forest.