A few points from someone who was in the firearms business (including police supply class III weapons) for several years:
1) DO NOT buy a pistol grip only shotgun ( I doubt you can in CA anyway) they are tough to hold and a 12 ga. round could break your wrist with the recoil. You want a stock that can rest the gun on your shoulder. Shoulders absorb impact much better then a wrist will.
2) A 20 ga. is sufficient and their are plenty of self-defense loads available for one. But a heavy twelve ga. is more then manageable for most petite women with lighter loads.
3) A shotgun at close range will tear someone up. The velocity fall off outside of forty yards is quite dramatic. But a rubber pellet load will knock down a three hundred pound lineman inside of fifteen yards.
4) The three biggest advantages of a shotgun are 1] the racking noise is as good as a doberman bark 2] If you are not using slugs, with shotguns you don't have a ton of penetration so it's not likely that you'll kill someone in the next apartment by accident 3] Shotguns, while I still recommend practice are much more "point and shoot" then a pistol and require less training. Most police shootouts are within seven yards and in most cases the guy who fires first loses. It's not as easy as Hollywood would have you believe to hit something with a pistol at twenty feet. I've seen 20% of the participants of a CCW class MISS COMPLETELY a man sized target at seven yards!
5) Never point a gun at anyone without the will and intentions to use it. Hopefully the gun will be deterrent enough, and in a vast majority of cases it is. Armed private citizens stop far more crime then the police in this country without ever firing a shot.
6) Do not look for "less then lethal" ammo. For the record a lot of police officers carry shotguns loaded with #4 shot, it puts more pellets in the target area then buckshot. If you (God forbid) have to use a firearm you want to stop the assailant, you do not want an assailant returning fire. Also less then lethal injury's have resulted many times in serious lawsuits. A criminal might sue you for "destroying his livelihood" if the injuries sustained prevent him from breaking down doors or climbing thru windows.
Absurd but it has happened, a dead criminal who was armed on your property when shot is not likely to sue.
Firing pins aren't cocking. 
Plugs (limits magazine capacity) are usually a hunting requirement. Take it out & fill it to max. Check laws.
