Very creative and refreshing approach on the challenge. Great lighting. Nice job.
The lighting and framing/cropping you've chosen draws attention to the hat, which makes it work nicely for this challenge, IMO.
Since the title indicates that the hat and not the child is the main focus, I would include the entire hat and maybe diminish her face. Although I wish she were in better focus. The shadowing on her face is well done and the glint in her eye is a nice touch.