I was hoping for a response to my questions. I don't think that medication is the answer unless there is an underlying medical cause for the aggression such as a thyroid condition. That can be ruled out with a thryoid panel done by your vet.
Otherwise, I think your dog needs training to help solve the problem. Here are sites on medical issues that can cause aggression.
If there is no medical cause for the aggression, then it is strictly behavioral. In that case, there would need to be a lot of changes made in order to bring this dog under control. Dogs are aggressive toward other dogs for a variety of reasons. It might be that they are fearful of other dogs and thus are aggressive before the other dog can be. In other cases, a dog is aggressive in order to dominate the other dogs and be the alpha member of the pack. Other causes could be that the dog feels they are the alpha member of the pack and as the alpha member they must protect the pack (you) from threats (other dogs).
In addition, owners sometimes make the situation even worse by tensing up and worrying about what will happen. The dog senses the owner worry and feels that he is justified in his aggressive stance because you are obviously worried about the dog. They don't know you are worried about them attacking, they just feel that you are worried and assume it is the other dog.
For a dog like this, total control is necessary. This means not only physical control but on a mental level, you must be the boss. To accomplish this, you will want to obedience train him or continue more training. If you can, I would do group classes (with the muzzle if necessary) and let the trainer know of the problem your dog has. It might take you a few months of basic training before she is ready for group class. . Before you can get into classes, I am including a link to a site that is very helpful. Be sure and click on the link to the left on obedience. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
You will also want to keep a leash on her at all times initially to grab if he should disobey. I think you will be pleasantly surprised at how well your dog does with training. Dogs like knowing what is expected of them and they love the little paper thin slices of hotdogs that I use for treats while training. Give this a try and see how it works for you.
In addition, if the situation is not improving using the techniques on the previous website, you may have to consult a professional behaviorist. You can usually find a behaviorist by asking your Vet for a recommendation or you may be able to find one using the following site.
It will be helpful if you can find someone with a dog to help you once you have your dog listening to commands consistently. What you will do is have your dog on the leash. You will have your helper off in the distance. Your helper will gradually move their dog a bit closer to you preferably walking past your position in the distance. As long as your dog ignores them, you can give your dog praise and a treat. The second you see him fixate on the other dog or show any other sign of aggression (hair standing up, etc.) give your dog a correction by giving a short tug and a firm low toned "NO". It shouldn't take your dog long to realize you will not tolerate the aggression and that if he ignores the other dog, he gets treats. Once this happens you can repeat the training moving the other dog closer until he is no longer trying to lunge at other dogs. You will need to practice this when you and your dog are walking as well.
Another method is BAT which you can read about here:
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer.