Clint, I feel for you. Nothing puts a knot in my stomach like not finding a hit animal. It happens though. When you do all you can as far as tracking, there's nothing left to do. We've all been there.
Congrats to your dad on a dandy of a buck.
And, you need to build you niece a bow, if you haven't done so already. She has woodman (woman) written all over her. She'll be hosting her own Outdoor Channel show in a few years.