A dead bird will be useful in the retrieve process. Keep your pup on a long line and under control during any live bird work to prevent them from catching them and developing bad habits. Granted, a live bird might help bring the "prey drive" up in a retrieve and might sharpen her up when it comes to retrieving. As for preventing her from chewing on the bird, keep her on the long line as stated before. Prompted the "fetch" command, let her go get it, and reel her in while being obnoxious about the "GOOD GIRL, ____" when she brings it back. Lots and lots of praise, and then take the bird/wing away. Make her feel special when she brings the bird/bumper back so that she is willing to bring it back and know that her reward is more you giving her lovin' than just the retrieve itself. She will start to work to please you instead of pleasing herself.
Before you just "get a shot or two in and whacking a couple", have you introduced her to guns? I would suggest picking up a few dog training books and some videos on how to introduce your spaniel pup to birds, guns, and general training. Follow a program, don't just "wing it" and hope for the best. As a dog owner (and hence a trainer,) you want to set up your little protégé up for success, not failure. I would get involved in a club or a group that can help you with hands-on in your area. A lot of people are willing to help, you just have to look for them.
Good luck with your pup,