Have you taught her "watch me" yet? It has been the single most effective tool in my working with my reactive guy. With a good watch me I can swiftly heel him out of situations that I have learned to predict will be a problem for him. Good face attention is really important in obedience work anyway.
Loose dog when mine is leashed? "Watch me" and turn the other direction OR move parallel with me between Huxley and the loose dog.
Runners or other groups likely to agitate? "Watch me" and move to the side and practice sits, stands, and downs ("puppy pushups")
You have to be aware of your surroundings but not reactive yourself. No tightening up on that leash. Use your happy voice and make yourself more interesting than anything else around. Keep stinky yucky treats on you for these situations.
Basically give the dog something else to focus on (you!) and another outlet for the energy (basic obedience skills) Be confident. Our dogs feed on what we emote.
Don't reward the behavior by soothing the dog. Try to avoid the functional reward too. This means you act before your dog has a chance to because if she is already going off and you move her away from what she is reacting to, that is a functional reward - meaning her barking/reacting worked as it got her away from what was making her uncomfortable. You really need to be aware of your surroundings, as I mentioned before, and find something that is good and correct for her to do before she can react poorly.
On a personal note, having BTDT myself, relax. Breathe. Have fun with your dog. I forgot that far too many times myself. These are hiccups in what will hopefully be a long and happy relationship with our dogs.