Regardless of whether it's an organised shoot or roughshooting any working dog needs to be introduced to gunshot and trained before they can work effectively and safely. If he wants her for hunting (flushing game) then at the very least she'll need to be trained to hunt and quarter in any cover, to stop to flush, to stop on the whistle and to drop to shot (lie down when she hears gunshot, this is vital for her own safety). If he wants her for retrieving/as a peg dog (labs are more often used for this though) then again at the very least she'll need to be taught to sit still for long periods while there is a lot of banging and activity going on around her and she'll need to find and retrieve both dead and live game to hand. Most spaniels now tend to be dual purpose, they hunt and retrieve, mine all do so they do all of the above.
Training is essential though, taking a young puppy, especially one with a nervous disposition out to a shoot and just suddenly exposing them to gunfire and all the activity there could scare them half to death and even if it doesn't they will have no idea what they're supposed to do and will undoubtedly be more of a hindrance than a help. Even if you are training your dog to work the worst thing you can do is to take them out shooting too soon, before their training is at a suitable standard; that's the best way to ruin the most promising young dog but unfortunately it happens a lot, people often get impatient with the training and take dogs out before they're really ready.
