I don't agree with the forum on this one, so I am jumping back in.
The guy behind the counter might be an ASSHAT, I think that's what you mean with azzhat, but this forum does allow some big kid words so I am using mine.

. We don't know for sure, we have your word on that, but maybe he was coached to say these sorts of things. We don't know.
Fact number one is the human female conditions' NATURAL instinct is NOT to kill. In fact this is found throughout nature when mom's of one species adopt other species that could grow to be a danger to themselves and their offspring. It's a biological trait, they are care GIVERS first.
Second fact is that the Israel has had problems with women in combat since at least 1986 that I can personally recall from the news of a raid gone wrong as a kid when all that mess with Libya was happening and The Bank again is dispute.
So this guy might very well have been towing the company line in telling your significant other that using birdshot will "wound" and not kill.
You might be married to the next Sarah Connor, although Ineffable has already claimed the young John Connor as his offspring, so you might be or you might not be.
Having said that the guy behind the counter doesn't know her from Bambi. For all he knew, she was the daughter of Haight-Ashbury Plankholders and would NEVER take a human life.
Now. Birdshot and distance.
Question. Do you honestly know what the term 12 and 20 GUAGE mean in relation to caliber??
In layman's terms? A 12 gauge is a 1/12th POUND of lead that fits into the weapons bore. So, in 12 guage buckshot, this means there are 12 balls of lead weighing approximately 1 ounce a piece and are 0.729" in diameter.
Birdshot is a variable of that same formula. #4 birdshot is 0.129" in diameter, but the quantity is still the same overall weight as the initial 1/12th of a pound, or about 12 ounces.
So, a shotgun doesn't expand much in 15 or 20 feet?
Good!!!
So we have thus:
#4 Birdshot is about .13" in diameter and weighs a mere 3.2 grains each. A 2 3/4" shell with a 1 5/8 ounce shot charge, there are
221 pellets with a velocity of 1250 fps flying in close formation your way.
If you think THAT is something to sneeze at, I would encourage you to pick up pig head, or a full chicken with the skin on, pace off 8-10 paces and see what damage is done by "merely birdshot"
JD