Will she drag the leash around the house ok? or does that also freak her out?
Does it matter if she's wearing a harness or a collar with the leash?
If you sit on a bench with her on the leash, not moving, but just giving her treats occasionally... will she quiet and let the world go past?
She may need more exercise...not sure though what else you have going on. So whether it's overwhelming excitement on the walk? Or fearful aggressive type behavior is really hard to tell over a forum.
Have you been able to get a behaviorist or trainer to see the pair of you? Sometime having the right eye see the issue can help right away.
Not sure why you care if she's out front on a walk. My dogs always walk ahead of me and usually I have one dog that prefers to be the most ahead. It's fine with me as long as I'm not getting pulled along. Think of a sled dogs pack dragging the sled, you think the human in the sled is thinking all those dogs are the boss? Let me tell you those dogs know who ultimately is in charge.
Have you seen the Gentle Leader harness
Bless you for going to a rescue and taking this on.