RJ,
Congratulations, a girl, 8 years old, and game to play --- good for her and good job to you! That said, she is at a tender point and with kids especially it only takes one miscue to derail them. While she is still at this very early stage, I too would recommend something in the .223 to .243 range if possible or a 410 or 20 gauge if she wants to shoot things that fly. She might out grow it in a flash, but it is an important stepping stone.
I like and lean towards the big stuff, but there is a time and place for everything.
Good Luck and Good Hunting,
EKM