A Malfoy and a Potter?

Carina Malfoy has always hated James Potter. She hated that he was arrogant, she hated that he used to bully her and her little brother, she hated that he never passed up the opportunity to hurt her in some way. So why is it that by fifth year James starts treating her differently? She doesn't know that he likes her, how could she? She's a Malfoy, and he's a Potter.