My Goodness, I am not an expert and have never been to a dog park because I live in the country so that's where I walk my dogs. However, I wonder if the grass had been sprayed with something that your dog found sickening and/or allergic. I dont know but I suppose you could go back one day when other dogs are there and see how Koko behaves. Maybe she was just overcome with all the smells and couldnt see the reason (other dogs) for the smells. I hope you find out why. Kay in NC