As much as I like 12 ga., it simply kicks far too much for petite wife, especially in a pump. I am currently saving my milk money for a HD shotgun and I'm 99% sure I'm getting a 20 ga. so that she can use it to protect herself.
Kind of sad, but I know a guy who told me, while showing me a brand new gun, "I bought this pistol for my wife to use for self defense." Problem was, his wife was 220 miles away. My response was, "Now, so and so, how do you expect her to use that when she's 3 hours away?" I think a lot of men use the HD firearm as an excuse to buy what they want....if we look deeply, and really care, we'd get something that every responsible person in the house is comfortable and knowledgable in using to defend themselves. And then we'd practice with it to ensure fluidity and competence in case something goes bump in the night.