I've never shot a shotgun...and I'm not sure I could. Are there any smaller ones for small women?
Yes, Ma'am!
I'm nobody's idea of a shotgun authority, but here are some basic facts, along with a suggestion.
Shotguns are measured in bore size. The standard American twelve-gauge barrel measures about .75" in diameter. The next lightest is the sixteen-gauge, followed by the twenty-gauge, followed by the .410, whose bore is about .4" in diameter.
Within each gauge, you can buy light, medium, and heavy duty shells, although "heavy duty" in a .410 isn't going to be anything like heavy duty in a twelve-gauge. Some shells contain a few round metallic balls of relatively large size, up to about a third of an inch in diameter, whereas others contain many round balls of very small size. The balls used to be lead, but they're now made of assorted non-toxic metals. In general, the larger the metallic balls, the more recoil the shotgun will deliver to your shoulder. In general, the smaller the balls, the less likely they'll be to penetrate walls and less recoil they'll deliver.
The beauty of a shotgun is that the criminal has no idea what load your gun has, and most probably won't be able to tell one gauge from another, but surely does know it's hard to miss with a shotgun, and the wounds tend to be exceedingly nasty. Fear is a beautiful thing in a criminal.
You don't need to buy a heavy, bulky shotgun and end up with a bruised shoulder to defend your life with a shotgun. I'd suggest visiting a well stocked gun shop and asking every "dumb" question you can think of, bearing in mind the only dumb question is the one you don't ask. Once you've tried on some guns for size and heft, visit a shooting range with guns for rent. Try a few shotguns and a few loads.
If you can't find a range with guns for rent, hang out at shooting ranges and start asking shotgunners questions. It's the norm for shooters to offer other shooters—especially newbies—our best advice and opportunities to shoot our guns.
Best of success, eh?