12 ga shot gun.
I would normally say a 12 gauge shotgun...but given her age and frailty, I would say a .410 shotgun...pump.....loaded with self defense rounds.
I think a 20 gauge would be too much recoil for her...and a 12 gauge would likely break a shoulder or arm.
I will say this....a good sized revolver shooting .357 magnum rounds will have less recoil than a small one shooting .38 special ones. My model 66 S&W has very little recoil with .357 mag rounds. It’s extremely manageable.
Concur. Debate about whether or not it should be loaded with bird shot or buck shot, but a short barreled shotgun remains the best home protection weapon.