text: After reading the other answers I guess everyone is right. I've used both and they each have pros and cons.\nYes a simi- can shoot again when you don't want it to. But they also help you get back on target faster for a 2nd shot.Double barrels can also fire a second shot in recoil, especially one with a single trigger. Both of these issues are controllable with training and practice.\nOver and unders have become the rage the past few decades, they do seem to point better than a sidexside but I'm not convinced they shoot any better. And since sporting clays started they cost a bunch more than they used to.\nIf your daughter  shoots her 20 ga. well she shouldn't have any trouble keeping up with the 12s. (Watch the Big guys at a trap shoot. A lot of them are using 28s or even .410 to cut down on recoil. They do fine) In plastic targets it's where you put the shot more than how much you put up. Granted larger gauges have more shot but if you keep the target in the center of the shot pattern you'll get the bird wheather the pattern is 20" or 40".Chokes are important too.\nMy advise would be to spend time at the range and talk to the people who are shooting. Many of the shooters are more than happy to give advise and I think you will find some that would even be willing to let your girl shoot a round or two with their shotgun. Usually you can rent guns at the ranges and that would be another way to see which style she prefers.\nThe bottom  line is gun fit and practice. Get a gun she likes. Make sure the stock fits her. And let her practice as much as she can.\n12 ga. should't be too much for a girl her age, but if it hurts her to shoot it she will never shoot it well.\nHope that helps.\nD