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 anime seem to like that kind.
Maybe it's because she fell in love 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 love 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 by those gentle, lonely eyes and then fell deeper in love with him from that point in.
