A gas operated semi-auto will recoil much less, and thus be easier to teach her how to shoot.
Checkout the CZ 720 Youth Model. It is a 20 gauge with a 24 inch barrel. Great reliable and soft recoiling gas operated action. The action, chamber, and barrel are all even chrome plated, just like expensive shotguns.
And you can order one for only $383:
http://www.budsgunshop.com/catalog/p...ducts_id/18307