Welcome to BPO. You will love it here. Is your dog growling at small dogs, big dogs or both? Is she growling when they approach her or you or both? Do you tense up when dogs approach, expecting her to growl? Obviously, the easy answer is don't go to the dog park, but that is not what I would do. I would start taking her to other places where she could meet and greet other dogs on a leash. This way, she can interact and you and the other dogs owner have control of the interaction. It sounds like you need to desensitize her to other dogs all over again. Basically, you take her for a walk, where there are other dogs. When a strange dog gets close to her, very matter of factly walk her by them. See how she reacts. If she doesn't do well, then walk her by them, from a great distance, until you find her comfort level and a point where she doesn't react badly. When you find that, reward her for behaving good and not growling. Gradually, over the course of a few weeks or so, decrease the distance between her and the other dogs, still rewarding her for good behaviour. This should help her to associate other dogs with rewards and give her a chance to regain her confidence and security in the presence of other dogs. Good luck.
Kathy
She mainly growls at big dogs, she likes little dogs. I always try to be relaxed and say hi to the approaching dog. She will let them come around but she likes to get between me and them. If they stay too long or start getting wound up, thats when she growls. Also if they get in her face she'll growl. You know how some younger dogs lick faces, she doesn't like it. The funny thing is we went to meet my boyfriends family and they have a boxer. He was all over her and at first she growled a little but shortly after they were running all over the place playing.
I'll keep trying to desensitize her. She's not on a leash much. When I walk her she stays close and stops at every corner until I tell her to cross. At the park it's an off leash area. But I'll try your ideas, thank you.