It's not unusual for comic book heroes and heroines to use guns. Lois Lane uses a tommy gun in the cartoon BILLION DOLLAR LIMITED,
and on the classic 1950's tv show in "Jimmy Olsen, Editor".
In another episode, "Beware The Wrecker", Lois Lane and Jimmy Olsen are able to capture one of the bad guys at his hideout with the aid of a rifle they find there. But neither of them actually shoots it.
They only use it to first capture him and then to hold him at bay in order to tie him up.
The bad guy is played by Denver Pyle, by the way.
In none of these was Lois Lane supposed to have killed anyone. Gratuitous killing was not supposed to be something that the good guys did in kid's comic books or tv shows in that period.