I'm taking my son for dove this weekend for the first time and have borrowed a 20 ga for him to try. I'm planning on using target loads. He's 10 and about the size of a 12 year old (4'11" 110lbs) but tends to be recoil sensitive. Depending on her size you might try a youth model.

Double check your local hunting regs. In CO you have to be 12 to hunt big game. Varmit and small game is OK, but either way you have to take hunter's ed. My son took it this year and it helped alot even though he has been shooting since he was 8. I'm cautious taking him hunting. Although he is very mature, he still is a 10 year old and I have to watch him closely. I am more concerend about other people's mistakes, though.

Best of Luck

Spud