Don't have guns. But I think maybe starting with a cap pistol- away from the dog to lessen her fear. Then very gradually move closer to her,so the noise is louder. Be reassuring and tell her what a good dog she is when she is calmer.
That's as far as I'd go. I'd probably be as upset over the noise of a real gun as she would.
You would need a good, professional trainer - that doesn't force or abuse dogs, to take over.
I had field trial Weimaraner, that absolutely loved to hear a gun shot. If you didn't shoot, it would try to bite the barrel to make it shoot! Took awhile to break him of that bad habit.
Also had a German Shorthair, loved that dog! You have a very nice looking one, too!