Thank you for the advice.
I agree that having the gun fit her properly and be balanced so that it isn't so muzzle heavy is of great importance, and also that working up from softer guns/loads is the way to start out.
Colorado, we are very much on the same page with regard to how important it can be to present things with the proper "can do" attitude, without focusing on the potentially unpleasant price of shooting fun.
Mojo, you aren't kidding when you talk about how fast they grow at this age! I've had her try the fit of some short-stocked shotguns, and she is already too big for the Mossberg 510 Mini. More than one gun store salesman has echoed your words that she'll fit a full sized stock in a few years.
She is almost big enough for the Mossy 500 Bantam now, but they don't offer the raised cheekpiece in the Bantam-sized stock, that is necessary to kee a good cheekweld and still see through the scope on a cantelevered mount.