Many of the above are right. You're better with reduced 12 than standard 20. I bought my wife a Benelli SBE II which has a kind of recoil pad built into the cheek piece of the stock. It really works. Slick gun. She's killed ducks, turkeys, and down to doves and skeet...
I'm a die hard pump guy, but when I hurt my shoulder last year during duck season I finished the season shooting her gun. I've got a safe full of guns... that benelli is the best combination of light weight, light kick, smooth action, and adult level killing power.