For a woman her first line of defense should be having her wits about her, then a well trained large breed dog. Then of course a good handgun that she can carry everywhere. Few ladies do well with a shotgun
As to breed we choose Rotties but they are a handful, full of power, attitude and stubborn. Best good dog IMO for a woman is a good German Shepherd
No one has made it past the front door at our home after realizing we "Had Rottie". They love fighting and horseplay. Imagine if he was really teed off
A couple of things;
1. Any woman can learn to handle a shotgun just as well as a man. It is simply a matter of finding one that is the correct size. If she is small in stature she may need a "youth" model but the overall size of the gun has no effect on the accuracy or effectiveness of what comes out of the barrel. If recoil is an issue there are reduced recoil buckshot loads available, or she can go down to a 20 gauge which is still plenty adequate for home defense.
2. The biggest, meanest dog in the world is no match for an intruder with a gun. All a dog can do in that case is take a bullet for you.
3. The best "watchdog" I have ever had....and I'm not kidding here...is a toy poodle. Mine is high-strung and alert 24/7. He sits on top of the couch and looks out the window and he will bark if anyone sets foot on the property. He will wake up in the middle of the night at the slightest noise while my other dogs remain sound asleep. He eats less than a handful of kibble per day and poops out a Tootsie roll. I dont want a dog that will bite anyone; I want a dog that will wake me up so that I can decide who needs to be bitten, and how hard, and with what.