Trying to escape the prong pushers

I met up with a friend from our Positive Reinforcement group we formed at the dog club (PR Partners) last Wednesday around noon to train on Sue Ailsby's training levels with her pup and my Velvet. I was planning to work on approaching a person without Velvet breaking the heel position. She has self control issues when it comes to greeting people and other dogs, she gets to a certain distance, and then she just starts like a rocket to meet them. There was another lady there, who had set up half the building with agility equipment. She had quite an old German Shepherd mix, who was remaining nicely in a down stay while she was still setting up some things. She was actually very friendly, and offered immediately to help out as a goal post, or with whatever we needed. So I said that I need someone to be my person I can approach with Velvet, and she happily agreed. I took a few steps with Velvet, and Velvet started breaking and tried to get to her. I did what I learned in Leslie Nelson's seminar, I gave Velvet penalty yards, ran backwards to where we started, clapping my hands, and calling her, and we set up again. Velvet was ready to go again, when the lady said "You know what would work great for a big strong dog like her.... a PRONG!". Immediately, I gasped for air, Velvet got up out of her heel sit and started pulling, sniffing frantically on the floor and we were just a mess. Talk about a handlers body language influencing the dog's mood!! Velvet must have sensed my shock ( I thought the lady was a positive trainer too). I said " Absolutely not" about 5 times in a row, and she went on to explain about how happy it makes the dogs to wear it, how the pressure is distributed evenly with a prong, and not as harmful as if they pull on a flat buckle collar, and she so much wanted to convince me, that I just didnt' know what to do. I just kept insisting no, and that I only use positive reinforcement, and her answer was "But the prong is POSITIVE!!! She was so nice all the while, but she did give up for now, and remained me goal post. Velvet and I composed ourselves and started up again, and I kept having to go back to the beginning about 3 times, and all of a sudden Velvet looked up at me, and when I slowed down on my way to the lady, she sat down, and instantly, I could walk around her in a circle, Velvet remained in heel position, giving me attention, and being in prime working mode. The lady was very surprised of the outcome, but I kept thanking her for being our helper, and it is no lie, I really appreciated that very much, because my neighbors are willing, but completely useless in dog training, because they meet Velvet halfway mistaking her breaking the heel for her absolute love for them, so they are flattered into rewarding her for her behavior. So Velvet learned a lot that day, and I learned that I can just say that I don't have the prong in my tool kit.