If she's actually been attacked, she may be afraid -- which is pretty natural. You must keep her from getting attacked or you could end up with a neurotic dog. Avoid dogs who are starting fight by leaving, if necessary. A puppy shouldn't have to worry about "defending" itself at a dog park--that's your job.
By the way, if she's avoiding aggressive, unstable or dominant dogs who might want to attack her, rather than fighting with them, that's a good thing. If she's trusting you to keep her safe, even better! If you ever see an actual fight in a dog park, you'll thank your lucky stars your dog wants no part in one -- a dog died in our local dog park that way. You do not want her to respond to dominance challenges by fighting back.