I put together a long and detailed response...but did it in spurts as time allowed during the day. When I hit post, it was all lost due to a time out...#$__=÷^%$
Anyhow, in the meantime Nigel brought up many of the things I was thinking. How long have you had the dog, does she follow you at home? Have you taught her what you're after at home without distractions? And several others that I am not going to type in again now....
But I will add that whenever you want a dog or puppy to go from a (where "a" represents where you're at now), to w (where "w" represents walking with you nicely on a leash), and you're having trouble with that, try breaking the "goal" into smaller, more manageable segments that your puppy can do and be successful at - a to d to k to s to w, for example...and if that still doesn't work break it down further!
Walking nicely on a leash is not something that comes naturally, there's always a learning curve. And more often than not, folks just see it as a given and just go. Spend some time at home eliciting the behavior you want to see on a walk, reward and praise and repeat often. Then go out, and you'll likely see a difference.
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain