Everything. Well, maybe not everything, but she is pretty much the reason Kirino and Kyousuke hated each other for years. That manipulative little freak didn't like how she herself was just a plain, boring and "normal" person while Kyousuke was a very good student, a fast runner and an overall very active person, so she brought him down to her own level (through some pretty sad and horrible phsychological actions which weren't disclosed in the anime, but only in the novels) and made him a lazy "normal" person. She was also the one who told Kirino when she was like 10 years old or so that she can't love her brother, and that her brother wasn't the cool person Kirino thought he was.
And her actions also indirectly caused Kirino to become the way she is now. I mean the selfishness, and the treatment of her brother.
tl;dr: She's manipulative. Can't stand those type of characters.