uncontrollable non-aggressive lunging on leash

Question
My dog, who I rescued 6 months ago (was told she was a year or year and a half at the time, so she may be going through the "terrible twos") is getting worse on the leash. She is very very friendly, plays hard with other dogs, loves other dogs and does not seem to get the messages they send her when they don't want to play, but it hasn't gotten her into any serious trouble. She's fine off leash (we go regularly to a dog run), and she has great recall and has never gotten into any serious scraps. But on leash, with many dogs (though not all) she lunges to play - not to fight, gets SO excited, starts biting the leash, and can not be controlled until the dog passes. I've been trying clicker training (clicking as soon as her head turns, then rewarding her with a high value treat when she comes back to me), which seemed to work a bit, but now the problem seems worse. I had her DNA tested, she's chow-chow/shiba inu mix, which might account for her smarts. Is there a way to get her to calm down when approaching other dogs? She's a great gal in every other way, doesn't seem to be manifesting the difficult aggression and territorial tendencies of some chow chows.

Answer
DNA tested! wow! I'm impressed.

Clicker training is a wonderful tool but...huge "BUT"...as John Fisher (the wonderful British behaviorist) used to say: "you know what you are trying to teach, but you have to know what the dog is learning."  You may inadvertently have rewarded a state of mind, a thought, an urge, that you would not have chosen to reinforce.  Additionally, the click IS the "reward", the treat is secondary; your dog may have actually received the reward for thinking : "Hey! Did you see THAT?" when she turned her head; or she may have been turning away for behavioral reasons (dog to dog).  She obviously did not make the connection between her LACK of attention and your click.  You need to go back to square one.

It appears that your dog has a common problem: total lack of socialization with other dogs through the first year of life (when she was not in your care.)  She cannot read dog language and cannot offer appropriate invitations to other dogs, presenting herself in an excited manner, not offering play bows, not responding appropriately to the body language (communication) of the dogs she is meeting, especially on leash (when restraint makes it more urgent for her to attempt to interact.)  You may very well be contributing to her on leash hysteria; this is nothing to feel guilty about, it is SO COMMON among dog owners.  The dog lunges (for the first time), the owner reacts with touch, or words, or (even more likely) anxiety; this all goes down the leash and complicates the dog's own excitability.  Then as the dog becomes more excited, so does the owner, and on and on we go, until there is a serious problem (sometimes aggression).  Forget the clicker for the moment (at least for this problem, use it to teach other behaviors as it enhances the dog's cognition and problem solving ability.)  Make a trial run with a good friend standing (discreetly) some distance away or walking behind you.  Have that friend evaluate what is really going on when the dog lunges: what are YOU doing to participate (unconsciously), how does your attempt to manage the problem AFFECT the dog's behavior, what aspects of this situation are you missing because you're in the middle of it.  While your friend is observing, the SECOND TIME you encounter another dog and yours goes ballistic, TURN YOUR BACK on your dog and walk QUICKLY in the opposite direction until you are at the end of the leash, then STOP.  Have your friend evaluate whether or not your dog stops HER behavior to WATCH YOU; this will determine how heavily your reaction is involved with her behavior.

Following this exercise, begin to use a Halti but use it in conjunction with the regular collar, NOT leading the dog by the nose.  After you have determined your contribution to the problem (from your outing with the friend), bring BACK the clicker and here's how to use it: your dog lunges, you already understand your contribution so you will NOT REACT in the usual manner, you will gently lead the dog by the Halti and her regular collar in an ABOUT TURN with a "come along" command, you will walk a few feet closely observing the dog and when her eyes are CLEARLY ON YOU you will stop and when SHE STOPS you will click/treat (immediately treat), then move forward.  Do this every single time she lunges for as long as it takes for her to begin to adjust her OWN behavior and respond to your "come along" command, which you will consistently offer.  AS SOON AS she responds immediately to the "come along", click/treat THAT.  NOW you have her attention, you know what she's learning, and you can teach what you choose.