Just went through this last year with my wife, an it sounds to me like the best gun for you is a 20 ga O/U with a 28" or less barrel. My wife is 5'4" and fairly strong (she pitched Fastpitch softball on the Div. I collegiate level), and even though she tried, she couldn't generate the speed needed with a heavy gun to hit fast crossers, she did much better with the lighter 20 ga. guns. All of the long barrel talk is good, and I shoot 30's and will be switching to 32's at the end of the year but I'm 6' tall and weigh 250 lbs so they fit me, but the gun has to fit you and your body and your strength. Yes, 1" of barrel equals only 4 oz's, but it's way out in front and can be hard to move for a new shooter. The other very nice benefit of going with 28" or even 26" barrels, is that you can buy them used a good bit cheaper than a longer barreled gun right now (for years 26" barrels ruled the skeet roost, and then fell out of fashion). The logic behind barrel length is that it's easier to point a long stick accurately than a short stick, and that's all well and good, provided you can control the stick. I really like new shooters to use an O/U as well, it is generally open when not on a station, and is rather safe. In addition, if you can find a gun with an adjustable comb it will help, there are several gunfitting issues that are very gender dependant so as always go see a gunfitter. Oh, and we ended up finding a great Browning Citori 425 for my wife, and she loves it, but take a look at the Beretta guns too.

Gordon