Well, according to the way the drawing is, it appears that Zara is the father's favorite. Perhaps he is more like common Disney villains, where he wants "Little" ones of himself. For example, "Little Scars" from a deleted scene in TLK. Therefore, Zephyr grows lonely and eventually cold-hearted towards others, or concealed around them. This would make her have more of a Scar tone to her.
Another idea, is that she'll do anything to impress her father. Zephyr will eventually have a small hatred between Zara as she grows older, since it was always easy for her to impress their father, unlike Zephyr.
I don't have any good ideas in mind currently, but there are two things for you to think about if you'd like.
