She's just at "that age". I have a younger brother and we hated eachother when he was 11 up until he was about 16. We get along great now though. Good news is little siblings don't stay monsters forever. Or in Howleen's case they do.
-- "Trust me. You're pawns of Orochimaru, and you don't wanna mess with Konoha Shinobi." Genma Shiranui.