I agree with DogMa and SlamDunc, the prong is probably too much for her. If the instructor won't listen or demands the prong, I'd suggest finding another instructor.
FYI I was shown a book recently, that was written by someone who was very respected back in the day, the trainer wrote how to deal with a dog that dug holes; he'd bring the dog to the hole, fill it with water, and hold the dogs head under water while it bucked like a bronco. This was repeated for several days, even if the dog hadn't dug anymore. Moral of the story, even bright experienced and highly regarded people can be very very wrong. We have to be our companions advocate and protector.
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