IF you have it to hand, and IF you get the hit (fast enough)
but you won't. and you wont have to, if you just ccw a pistol around, that's plenty. so the shotgun is bs. that "rathole effect only works to about 10 ft of range, which is nothing much in the way of "reach" and the fact that it happens means that you could have used the rifle, the narrow patten of shot was little or no help at getting the hit. those are a lot of limitations.
My wife will be getting a 20 ga pump gun, tho, cause she'll need to be able to teach the splattergun for those students who just won't listen. She'll also have a .22lr bolt action and a 357 Lever (at least for a while) while she learns the limitations and uses of those types of actions. Ditto a M748 Rem in 308, cause we'll be living in elk country and cause she'll need experience with the big club, too. Same reason that she'll have a 1911 govt model .45. An Armscore, from the Phillipines. Cause they're plenty good enough and they are sub $400, with nearly all the mods already done.
She'll also have to have a glock 19, a sig P239, a Kahr 380, a 3" M36 smith, her ccw P938, another Sig with a Sig .22lr unit on it, maybe even some cheapo .22lr SA revolver, just for the sake of completeness, altho having to 'uncock" that hammer is a damned unsafe thing to be doing.
Gunkid, seriously getting her started with a 20 gauge is NOT a good thing, my wife found that it still has a fair amount of recoil and caused bruising. Find her a 12 gauge that she is comfortable handling then buy her some 12 gauge #8 shot Winchester "AA" "Low Noise,Low Recoil" ammunition. My wife fires over 500 rds of it a year with no complaints (and that's what keeps her shooting). It only has an MV of 980 fps vice the average MV of 1145 fps. When she gets happy there then move up in shot size.