Sound as we know it, can't travel in the vacuum of space.
I always "explain" the sound of the ship, and the weapons in space as the sound the people onboard hear, through the air inside their ship.
Exploding the death star, or anything else is space would only be "heard" by the people onboard the exploding vessel.
Film directors, however want/need something both spectacular enough to entertain and familiar enough to be understood by the masses.
If Vera needs oxygen to fire, then whatever it is that she does fire is NOT a self contained cartridge.
One of the traps of sci-fi is that if you make up something, and give it a set of characteristics, based on what a character says it does, or how it works, you cannot go back and change that. A later episode (or a different writer) might want something different to better fit the current plot, and changes something without staying within the logical parameters set in earlier episodes.
Continuity flaw! boo!