aw, it does sound like she's a sweet dog, growling does not always mean she's being aggressive... it's usually just a warning, and totally common in dog language. I'm sorry I dont have any good advice. Being a ball crazy dog, Gonzo can also be a brat with other dogs chasing his tennis balls and he'll bark at them. He's a total show-off. The only way we prevent that is just having plenty of tennis balls at the park, so if a dog steals his he knows there are others around. Obedience could help a lot, as far as your being able to control her when tennis balls are involved... once she has a solid recall, you can call her to you and distract her if you sense a scuffle coming on... I hope you find a solution A behaviorist/trainer would have much better advice for you!