Hello Zack,
Thanks so much for the kind comments and for taking the time to write me a question. Your question basically is " I have a young gyp and she'll trail a pig hide or ear but she wont show any aggression to a pig in a pen I've let her watch my older bay dogs and she'll yap a little but I haven't put her in the pen because of her not showing any interest."
Well Zack, the key word you say there is YOUNG. You don't say how young, but the main thing to understand is each dog will mature at their own rate. I've had pups that would bay hogs from the out side of a fence and were just a couple 2-3 weeks off their mother, and I've had others that never ever showed the slightest interest until they were 18 months old. Heck, one "give me" dog that was either going to be culled or given away I took and got interested in hogs and he ended up being one of the best I ever had and he was 3! But I knew his breeding top and bottom throughout.
I guess what I'm saying is, If your dog has it in her, time is one your side. Problem is, most folks don't have the patience to wait one out. Lets not look at the failures so far of her not barking, lets look at the success. Your getting her to trail a hide/ear. Now that's wonderful! There's a lot more out there that will bark like the dickens at a hog in a pen and wont make the first step towards hunting a scent down like yours is doing. I call them a "me too" dog. Which means the dog is saying to him/herself, I will help you out at the bay, but I'm not going to go to the trouble of helping you find the hog.
Next thing, Let me say this. Don't let how your dog does in or around the pen be your judging of your dog. The WOODS is where you judge a dog for hunting. Some of the best woods dogs I've ever owned or ever seen either wouldn't hit a lick in a pen or would make you embarrassed if you took them to a baying contest. On the other hand, a few of the best woods hunting dogs I've ever owned did great in a pen. The bottom line is--not all dogs will bay in or around a pen.
If your determined to get your dog excited around the pen, tie the dog to the outside of the fence, the pen needs to be small, maybe 40' diameter or so. Work the other dogs in the pen, maybe even letting them catch to get the hog to squealing etc... The dog should eventually start. The dog I mentioned above that was 18 months, I actually gave patience to way to long, but one afternoon in doing what I just mentioned above, he just all of a sudden started. Next day, I did the same thing, he got fired up, I put him in the pen with two other dogs, they caught, he caught and from that day forward, he was what I consider a real rough dog on a hog which ended up being his demise in the woods.
In the woods, If you hunt with others, hold your dog on a leash until their dogs find the hog, when the hog is located, turn your pup loose to go to the bay. Usually the excitement of this will get your dog fired up after a time or two to where she's baying at the bay. You can sometimes achieve the same thing by tying out a hog in the woods.
Main thing is to have a bit of patience with the dog. When all your patience has run out with the dog, give him one more chance after that :-)
Good luck with your dog,
Jim