Considering that the Beretta is a pretty big gun, she probably would have had a .357 wheelgun if that's what she had been restricted to. The perp would be just as dead.
Of course the perp had a 9mm semiautomatic too, but I guess wackos aren't restricted the way security guards are. Sheesh.
Some Berettas are bigger than others. I have not been able to find what model she had, or what the capacity of the magazine she was using was.
It is pretty clear that it was a Beretta 9mm, though.