I'm so sorry you're having to deal with this. What little I know is (1) you have a big problem, and (2) it's going to take special training to get your dog through this. Basically she's going to need a program of careful distraction and rewards until she learns to deal with other dogs.

This fear-aggression is not uncommon, so there's literature on it. You might also want to contact a trainer specifically for this purpose. All the training you have already done with her will help a good deal because you need that basic control first. Good luck of course.