Search this forum for "reactive".
Your dog is "dog reactive" meaning she feels the need to notice and bark at other dogs. You must teach her that that is an inappropriate response. Generally this is done by not letting her get close enough to other dogs to trigger he reactivity, and when she does first notice them without reacting, re-focus her on you with treats and gentle correction. As she gets used to the idea she will realize that whenever she sees another dog the proper response is to look to you, not to decide on her own that she needs to bark at the other dog.
You will have to be disciplined yourself to be on the watch for other dogs getting within your dog's tolerance perimeter, and thinking ahead about stopping and re-routing your walks so you don't violate that perimeter before your dog is ready.
Once she gets the basic idea you will find that you can shrink the size of that perimeter fairly quickly, until you reach the point that your dog can sit at your feet while you hold a conversation with another human with a dog 3 feet in front of you, and your dog will ignore both of them. It takes lots of consistent training on your part, however.
Liesl, b. 1/1/11