Amy, don't listen to most of these assclowns. They didn't even qualify you, where you live (in a rural or urban area), your stature and whether you've ever shot a gun before or not.
First... Some women can handle any gun a man can and some cannot. This isn't sexist, it's pure logic and dynamics of body weight and upper body strength. So if you're a bull dyke and have extra testosterone, a bigger gun won't be an issue. My wife for instance, she's a dead-on shot and she can handle up to a .45 hand gun and just killed it with an Ak-47 out on the range last week. However, she didn't care for the 12-gauge shotgun or .30-06 rifle because of the kick with both.
Second... What is your living situation and area to defend in? If you are in tight quarters, apartment, etc., a 20-gauge shotgun will work just fine. In fact, just the clacking of it will give whoever is breaking in second thoughts to stick around for the BOOM that follows. Chamber it with #2 or #3 buckshot and you'll do some serious defense and damage.
Third... Read what this guy has to say... He's smarter than most people I've spoken with and if you follow the links at the bottom of this link, you'll find just about all the information you'll ever want on guns. [link to www.chuckhawks.com
Lastly (my two cents)... Guns are subjective to a great many factors. My perfect combination might not be your own, but it doesn't mean it's wrong.
We have a Remington 870 20 gauge (although I would have went with a Mossberg 500 or Beretta Xtrema II (Watch this clip and you'll understand why). Beretta CX4 Storm (.40 S&W), Beretta 96FS (.40 S&W), ATI GSG 522 (.22 LR), SIG P226 (9mm), Judge 410 (.45/.410 shotgun style shells) and I load hollow point in most of them because of the stopping power PLUS hollow point won't go through people and keep on going (like hitting someone else behind them. I went with .40 S&W on two of them because I anticipate there being plenty of it to pick up off of dead bodies in the apocalypse.
That's it... Good luck in your decision.