Personally I'd stop going to the dog park. She's scared, looking to you for help, and tough love is not going to solve it. What she'll end up learning is to solve it herself if another dog approaches her before she's ready, and her answer will be aggression.
I've been working through similar dog issues with my puppy (currently 5.5 months old, started around 4 months) though in my puppy's case I'm not sure what triggered it as she's never been attacked or bitten by a strange dog. We've been working on both classical conditioning (technically counter-conditioning in this case) a positive response to the sight or sound of other dogs, and operant conditioning engagement.
With the classical conditioning, I have treats ready and as soon as she sees or hears another dog, I pez-dispenser them into her mouth. Dog = great treats. This works to change the underlying emotion from dog = scary to dog = great. I also reward her for choosing to look away from the dog and back at me (the operant conditioning/engagement part) so she doesn't just stand there staring at the dog. We've been working on this for over a month now so she's definitely made progress, along with not forcing (and in fact avoiding) direct interactions and greetings with other dogs.
Might be a good idea to find a trainer to help you with this. Should probably discuss it with your puppy class trainer. What kind of puppy class is it? Is it kind of like a basic obedience/manners class, or is it a free for all puppy play class? If it's the second I'd drop out.
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