Which just goes to show that she really doesn't know anything about movies. By the time the seventh movie comes out the majority of audiences (the majority being made up of non-fans and casual movie goers) will have forgotten about whatever chatacter was introduced here and would need to be introduced again anyway. If said character wasn't needed in OotP, they shouldn't have been included, it's just dead weight (my guess is, she's talking about Grawp).
It was her idea to include the Whomping Willow scene in Chamber of Secrets, a scene that most people wondered what the hell was doing there as it did nothing for the story, plot or characters and just seemed to be put in gratuitously. She probably argued that it was an important story point in Prisoner of Azkaban, but Curón had to re-introduce it there anyway in the form of the small insert of the bird being killed by it, so it really was unecessary.
There's no doubt JKR gets a little input, but she gets a hell of a lot less than she used to, the studio's learned the difference between a decent book adaption and just plastering everything from the book to the screen to please the fans (which is essentially what the first two movies did).