I added a comment but I'll add an answer as a possible soultion too.
I'm going to be honest with you, leash agression is usually due to being poorly socialised on walks or outside from a young age. You have personified her slightly as dogs don't think like us humans and thus can't be agoraphobic. She is unsure and is therefore scared.
Snapping and lunging is never out of excitement and is definitely a huge hazard she can kill other people's dogs which unfortunately is much more important than her discomfort!
To try and ease the severity of her reactions you can try these steps:
Step 1 - Adding leash and dog friend within a building
To start just attach the lead to her when she's inside with a new dog friend. Allow them to play, relax and just generally enjoy with each other for an hour or so every few days. Take note of any toys your dog seems to prefer, you'll need this in future steps.
Step 2 - Progressing to both dogs in yard on leash together
Once both dogs are calm and relaxed with each other inside the building progress to a yard or garden with them and do the same thing, ensure they have toys they can play with and/or treats. This helps with taking the attention off the dog. Only give the toys if the dogs are relaxed or you may accidentally reinforce bad behaviour.
Step 3 - Walking down the road with both dogs
Now for the big one, once both dogs seem settled pick a time where you believe there will be no other dog walkers around and take them for a brisk walk up the road. Ensure you have your dog's favourite toy to reward any preferred behaviour from them.
Step 4 - Meeting the friendly dog outside
Have the friendly dog come and meet your dog outside your house. They should be familiar with scents by now and therefore shouldn't show any negative behaviour. For any desired behaviour ensure you reward with a toy or treat.
Step 5 - Interacting with other dogs with friendly dog interacting
From your comment that she's already fought/snapped and barked at previous dogs I would put the muzzle on for everyone's safety and peace of mind when starting this step. I would also take the friendly dog on the walk so that your dog can see (and learn) an appropriate way to interact.
Step 6 - Progress to walking by herself
Regardless of how well the previous step worked I would once again put the muzzle on her until I am 100% confident that she is showing no aggressive behaviour towards other dogs. As the last thing you want to happen is being the cause of a fatality. Using a similar method as before simply walk your dog as normal. If they display any aggressive behaviour give them a firm "NO" and continue walking. Do not fuss, do not pull back, don't walk towards the dog just continue in the same direction you were going to begin with. Once she stops being aggressive and is no longer focusing on the dog, reward with a toy or treat.
If you move onto the next step and it doesn't work revert back to the previous one. It may take some time and lots of patience but don't let this discourage you. It takes time to work anxiety out of dogs.
Side note: It's also important that the dog friend you use is not aggressive toward other dogs at all otherwise it may worsen both of their behaviours.