Just for fun I’m designing a jackxsally fan kid. Doubt I’ll make her an official character of mine, though we’ll see. Just inspired to try making them a fan kid to see how I do. In my version, Willow is made like how Sally was. Since Jack is a skeleton I believe it is impossible for him to produce children. But that doesn’t mean he couldn’t have doctor Finklestein make him a child. Thus explaining why her eyes look the way they do. I imagine that because Willow looks so much like Sally, Jack would want to put a bit of himself in the mix by giving her clothing similar to his.