Hey KYTrapper,
What age are you current beagles? I generally pair a green pup with an older dog to start off. The pup will learn from the veteran, and for the most part, he will be better able to keep up. Most of my beagle pups "break" around 4-5 months of age, depending on when they're born.
Make sure to pick up a good quality coated nylon safety collar for the pup, along with a beagle bell to know where she's running.
It shouldn't take more than a couple of trips for her to pick up on the idea and to get with the program. Start her in an area where you don't have to worry about her running across a road in pursuit of a bunny.
I've never used training pens, never had the need. If you current mature beagles are too fast for her, ask around to see if you can't partner up with someone who has a GOOD, older dog. Be careful she doesn't pick up bad habits from other dogs. Don't depend on what the owners will say, 'cause most will BS you on how good their dogs are.
Since she is a pup, you don't want to hunt her too long, especially in hotter temps. By October, I'm sure she'll be well on her way to becoming a great little hunter. Hope this helps.