heterochromia, I was like "Wooooow" when I first noticed. I've never seen such beautiful and unique eyes. Apart from that her whole character is unique and she's such a sweetheart.
The only one thing that only slightly annoys me about her is that she cannot distance herself emotionally from some matters, especially if they concern her friends. This is not a flaw in itself, but it gives her so much more to worry about in life. However this is probably just the INTP speaking.