Oh dear. So sorry your girl has had some bad experiences lately with other dogs. It can take many, many positive ones to recondition and get back on track.
For a while, you'll have to speak up on behalf of your dog and explain to other owners that if your dogs are to meet it must be a process that looks like this:
1) Parallel walk. This means both dogs on leash are walked together at a brisk pace. Neither dog is ahead / behind, but rather are kept parallel. Distance apart is dictated by the dogs' signals. Any tension, staring, barking means move them further apart, they are "over threshold" and too close for comfort. Once you see the dogs sniffing the ground and taking their eyes off one another you know you are at the correct distance apart and are making progress in the introduction. You can gradually move the dogs closer, continuing to walk, as long as you are seeing the ground sniffing, forward looking behaviors (or as long as the dogs are not staring at eachother, barking, etc.)
2) Close proximity = reward and relax. Once the dogs have walked side by side and almost seem to have grown bored with one another, it is time to rest with the dogs in close proximity. They will not be encouraged to meet yet, but will instead interact a bit with their individual handlers. Offer a treat or 2 and massage & pet to build the association that being close to another dog means good things happen.
3) Off leash interaction.
First, my rant about why off leash..
Leashes ruin everything!!! The first time your dog really interacts with her new friend, you want both dogs to have total freedom of movement both to retreat and to express the full range of body language dogs use to communicate. Owners will often feel much safer with their dogs restrained by leashes when greeting a new dog - what they don't realize is that leashes
cause problems instead of providing an easy solution. Dogs feel restricted and therefor automatically more defensive on leash. Their ability to get away from the situation is reduced so by taking away their flight option we leave them only with 'fight'. A too tight leash can prevent the dog from displaying low, wiggly greeting behaviors meant to convey the message to the approaching dog "I'm friendly and harmless" and instead can force the dog into a posture that says "I'm looking for a fight". Leashes WILL get tangled if the dogs perform the proper greeting ritual which I will describe later. Owners want the safety net of the leash so that they can rip the dogs apart if a spat breaks out. But this is not a good way to break up a fight anyway. Especially with small dogs like the OP references, leashes are totally unnecessary in getting 2 dogs away from one another should one or both get snarky. My preferred method in such a case would be to place a large object between the dogs to first break their visual and physical access to one another. Then each handler can either herd (like a border collie!) their dog back away to a safe distance from the other dog or physically move them away and
then clip leashes back on the dogs once they're apart.
Now onto what the off leash greeting should look like. It is a beautiful thing really that once you see hundreds of pairs of dogs do it becomes like a familiar movie. It plays out basically the same way each time. The greeting will typically start face to face but should not linger in this region, sniffing should promptly move in an arc, with noses following the side of the other dog's body and ending up at the rear. When you see the dogs sniffing each other's behinds with their bodies in an arc shape, you've reached the last step of the initial introduction ritual. That face-side-butt sniff is comparable to the human handshake. It is a "nice to meet ya my name is ___" for dogs.
So after the arc sniffing ritual is done, you might see any range of interaction between the dogs. They may both "shake off" and have little interest in playing. They may offer play bows (lowering the front end and sticking the rear in the air) and run and chase. But if you've spent the time on Parallel Walking and Close Proximity Reward & Relax (1 & 2 above) you shouldn't see much in the way of teeth baring and air snapping at this point.
I want to give you a simple protocol for 'fixing' fear in dogs. This protocol can be applied to many situations but I'll use fear of other dogs as my example: (This is based on the BAT protocol
Behavior Adjustment Training (BAT) | Official site for BAT: dog-friendly training for reactivity (aggression, fear, frustration) by Grisha Stewart, MA ,
BAT « Ahimsa Dog Blog )
1) Expose below threshold. So in our scenario that would mean taking your little dog somewhere where she'd be guaranteed to see another dog, or arranging for another dog to be in a specific location. You'd have your dog at a distance away from the other dog that makes her feel comfortable enough to display calm behavior. If she is staring at the other dog, whining, barking, pacing, or exhibiting any tension - you are too close and need to move further away from the other dog. Once you've found your safe zone, you are ready to begin working.
2) Wait for or manufacture an acceptable behavior. Acceptable behavior is defined as anything other than staring, barking, lunging, pacing, and other nervous behavior. You can wait for your dog to sniff the ground, look at you, sit without being told - and then do step 3 OR you can manufacture an acceptable behavior my making a kissy sound so that doggie looks at you and then move to step 3..
3) Mark the acceptable behavior with a clicker or a verbal marker like "good!" or "yes!" So in our case it would go: dog sniffs ground or looks at handler, then we mark that good behavior with either a clicker or a word like "good!" and then we do step 4..
4) Give functional reward (decrease stimulus intensity). In our scenario that will mean moving even further away from the other dog.
5) Give a bonus reward. Treat or toy whichever is preferred by the dog.
You'll keep repeating these steps and should be able to get closer to the other dog gradually. Even though writing out the steps this way makes it look like something of a process, the steps should actually run pretty rapidly one after another once the dog is under threshold and displays an acceptable behavior.
You might want to start your rehabilitation with the BAT protocol above and once your dog has success with it move on to the first method I explained and have her meet a new dog. Choose wisely of course as additional negative experiences will only compound her issue.