my crazy theory which could be easily disproven:
Naruto is the long lost brother of Ino, given up for the "Seal the Kyuubi!" cause. since Naruto and the Yamanakas all have blonde hair and blue eyes, they could be related right? Add in the fact that none of the Yamanakas ever speak badly of Naruto... Ino just doesn't like him, cos he's not 'Sasuke style' enough