Sometimes the walking bit is only a small part of the training problem. If your dog doesn't have all of the basics down pat and is good at listening to you without distraction, it doesn't have a hope of listening with distractions.
She might get some really good results if she begins again - treating her 3yo dog like a puppy and going through all the same steps.
It's like "re-setting" the dog.
I did this with a rescue/rehome and the results were slower than that of a puppy, but it made a huge difference.
Start with Sit, Stay, Come when called (at home) and progress from there. Build on the basics. If the dog doesn't respect boundaries at home, it won't respect the leash out on a walk.
Please let us know how you go :-)
Asha - 22/05/15 Wolfhound cross a Dogue De Bordeaux X American Bulldog.