I went to a dog park against what I was taught and lost control of my dog.

I did it. Went to a dog park. Against what was taught in the course. Everything was great for 2 months. My dog is a European Doberman, female, 1-year-old. Needs a lot of exercise. Today, she is great at the park until a woman shows up with a ball and a long stick for throwing it. My dog is excited, chases the ball, runs back to the lady, and jumps on her. She starts yelling and swinging the stick, kicking my dog. I'm running to grab my dog as she thinks the lady is playing. Not good, my dog jumps at the lady and nips her in the knee trying to grab a toy. I'm in front of the lady trying to calm her and get her to stop yelling, swinging her ball stick while my dog is circling us. She is finally distracted by another dog to play with. I grab her and exit the park post haste, my hands trembling so badly I could hardly get her prong collar on. How did things get crazy so fast? How can I make sure this never happens again, aside from not going to the dog park? Help.