Don't forget, intact females have good reason to be aggressive particularly after a heat cycle. If she were bred (and her body pretty much tells her she has been- contact with male or not) she must eliminate all threats to herself and her future young. Aggression toward adolescent dogs, and other females is par for the course.
When you chose to keep a dog intact, which is a perfectly acceptable choice, you also for the most part are choosing against dog parks, random dog-dog social interactions. And you are choosing, at the same time to have far greater control and responsibility, particularly with an intact female who comes into heat twice a year and will do her best to get bred.
Intact female shepherds, in my experience, have the highest rate of dog-dog aggression, particularly during and right after a heat cycle. If you don't like this, and don't plan to breed, spay her during the hormonally "quiet" time of her cycle.
Otherwise, plan to use quiet, public lands (Nat'l forest, BLM, state forest) to exercise your dog because this behavior is more than likely going to escalate with subsequent heat cycles.