As above said, but also when your dog freaks out do you try and clam down by patting her, picking her up or sweet talking her? Any of these responese just re-inforce her already confused mind. I would definantly try taking her to some dog classes, try and find one that knows dog physcology and not just sit, stay, come etc as there is a huge difference in understanding a dogs behaviour to just teaching it a few commands. I would also try distraction to help keep her mind off other dogs that are appoaching, does she love a particular toy that she will focus totally on and watch it instead of the other dog? My old dog Sam was MAD about tennis balls and would ignore thunder storms and fire works just to play with a ball. Or perhaps your dog is food motivated, or has a favourite stuffed toy. Also what type of dog is she? The breed can often determine how best to work around its "bred for genetic make up" , eg. working dogs have a strong desire to chase and herd and go mental when not given the stimulation they want, a walk for them is just not enough, while a sledge dog was bred to pull and believe me they enjoy nothing better than running at speed with something in tow.
I would also find out more on the breeders set up, did they keep all of their dogs seperate all the time? Where the pups only ever with their mother and thus never knew any other dogs?