Be Patient. Rescue dogs take time and patience to heal. Some never fully leave their past behind them, and that is okay too. Know her boundaries and let her test them on her own. One of my big dags is still fearful around men (she was beaten quite badly as a young pup), but she has come around to 'accept' when men are around without reacting. I hope in time she grows out of it completely, but all you can really do is encourage good behaviors and be a good pack leader. Every dog is an individual, just love her and support her and you'll end up with a great dog, regardless.
~Kat