It's extremely hard to come up with an answer to this question.
Maybe it's because he was a princely figure, and most girls in animê seem to like that kind.
Maybe it's because she fell in amor with him the moment he saved her from the ravens.
Maybe it's because she was told that her father and Mytho were the only people who would amor her and she was grateful for the prince's "love".
But the guess that I favour is that, just like Ahiru, she was taken in por those gentle, lonely eyes and then fell deeper in amor with him from that point in.