A couple of thoughts here -- one, get a prong collar. It is a self-correcting collar which should be fitted at the mid-point of the neck. Do Not jerk on this collar in any way. As she moves against it, she will put pressure around her own neck and will come to realize that that is no fun and slack off. I've recommended them to many of my students and had great success when they're used properly.
Thought two, begin a program of desensatization or distance socializing. What you do is take her somewhere where she can see people doing all kinds of things such as a park or mall but keep her at a distance from the activity praising her quietly so long as she behaves. SLOWLY, move her a few feet closer and keep praising as long as she behaves. If she begins to misbehave, stop the praise and back up a bit. Once she settles again, beging the praising again and let it go for the day. We have a tendency to be very strong with negative responses, so don't respond negatively as that will reinforce the "bad" behavior even more. Don't let anyone approach her for a good while as she will see this as a threat. If you ever notice when dogs approach each other, it appears as though they get up on their toes and hold their heads high -- it's a dominance thing. What your dog is perceiving is all these quick-moving, potentially dangerous, dominance things approaching and she's going to let them know early on that she's not going to take it. Kill or be killed, so to speak.
The muzzle might be a less than great idea as she will come to associate it with being around scary things and it may negatively reinforce the behavior you're trying to prevent. One-on-one professional training is a possibility, but make sure you like how the trainer acts around your dog and you. The more the dog can get out and about and get praised for good behavior the better she'll be, but go slowly and quit while she's being good. She will eventually realize that not everyone is out to hurt her and will learn to trust you and your judgement. It'll just take time.

[This message has been edited by ktreva52 (edited November 15, 2000).]