RE: need help picking a gun
Get a break open 20 guage like a H&R or simular, get a good recoil pad and some weight to put in the butt. The H&R ultra slug guns come with a steal bar in them. Shouldn't be too hard to pick one up and stick in there. It works pretty well.
Then let her shoot some light field loads. That should work ok. They make inserts as well so you can shoot 410 shells out of them if you want. However from what I understand they are not very accurate at all.
If she has never shot before I would suggest starting her out with an air gun or a .22 that isn't loud and doesn't have any recoil. If you start her right off with a shot gun she may never want to shoot it again or devolope some very bad shooting habbits from flinching and the what not. All shot guns kick to some degree or another, it just depends on how well a certain person handles it. Some don't mind, some the slightest recoil frightens them.
I started with a 20 guage H&R that was pretty light. I weighed about 80lbs and liked shooting 3 inch shells out of it. It about knocked me down when I pulled the trigger, but I thought it was fun. Someone else may not feel the same way, especially a small girl. See if you can find a friend that has some different guns she can shoot to see what she can handle.
Honestly I wouldn't give an 8 year old a loaded weapon in a hunting situation. I would want much more control over the situation until I was confident how well they handled themselves. Maybe if it was out of a blind and I knew they could shoot well. I know many will dissagree with me, and that is fine. I am just saying what I would personally do. I am in no way telling others what they should do with thier own kids.
Paul