Is that a rifle?

The object has (understandably) been mistaken for a rifle or a shotgun, but it's actually an umbrella - you can see the tips near the nun's right hand. The nun pictured is Sister Celestine, who was the school's music teacher and band leader; she was played in The Trouble With Angels by Binnie Barnes. However, there's no scene in the surviving film of her with an umbrella, so I'm not sure where the image came from - maybe a publicity photo, or a sequence that was cut.

I'm almost positive it is a photshop remake for the DVD release. There is no scene in the movie with a gun. It could have easily been a scene where some nun had the job of shooting off the birds in the orchard or something, but not part of the movie.

The the sequel there is a scene where the nuns and girls are fighting of the "indians" (they do not know they are in the middle of a movie set), and there is a gun invovled. That is is the closest.

on the dvd, the opening menu picture, there is a nun riding a bicycle with her legs kicked out; she looks like she has a beard! maybe the beard and the rifle are just bad art work.