excellent shot and for me, as a family type of guy, this is what it is all about:) The one weak point, IMO, is the angle of the face leaves the left side of her face slightly out of focus.
But, big deal... still a great shot and a beautiful girl.
I would imagine that if you were to take a portrait of her when she's 20 with same pose, same hair etc. it would be hard to tell the difference. I think what you see is a young lady rather than the little girl that you know. I love the purple in the background and for me the softness that is in question looks like a very shallow DOF but you got the lips and eyes spot on, I actually like it.
It is a great look and candid. What lens were you using if I might ask? I like that you got in close, it gives it a personal touch.
My only issue is the softness.. not that it *is* soft, but the type of softness. In this case, it looks like camera-shake to an extent, or noise that you've over-smoothed? Anyway, something about it just doesn't look right for the type of portraiture. It's a small thing really, as the expression of extremely subtly mischievious mirth just puts a smile on your face.