Pulling and nothing works

I have been trying unsuccessfully to teach one of my dogs to stop pulling on her leash for about two long years now. I feel like a bit of background might help. She is actually my boyfriend's dog and was raised being allowed to pull to her heart's content until I showed up. Now she will just about drag us wherever she wants to go, and we're no push-overs. I've read and tried every suggestion and how-to I can find; I've tried half a dozen collars, halters, and harnesses. Nothing works, not even stopping and backing up every time she pulls, which is apparently magic for most pullers. She just lunges forward again and barks in frustration when told to sit. She even learned how to brace her head against a Halti and just keep going. Now, I will admit that progress has been made, but a plateau has been reached at arm-not-being-pulled-from-socket. I believe the "problem" lies in Sanzie's motivation. She is not a "typical" dog motivated by pleasing her owners and couldn't care less about food during walks (any other time is a different story). The only thing she wants is to run and refuses to accept anything that tries to slow her down.
Please, does anyone have any ideas what I can do? I am at my wit's end and just want to enjoy going on walks for once.

Several of those methods work IF you are consisent and you don't give up. Giving up and bouncing from one method to another is a big downfall of many people trying to teach their dog to walk on a loose leash. I prefer to stop for 10 or 15 seconds and then take a step backward, 10 or 15 seconds take another step backward. Your dog has to learn that no forward progress will be made EVER if she pulls. The ONLY way forward progress can be made is on a loose leash. This means that on early walks, you may not make it to the end of your driveway. Evidently you are not being that consistent. You are letting her win too easily.

Don't try to do this with more than one dog. You must be walking that one dog only and not any others. If you have a dog that is good, walk it seperately until your dog is reliable with loose leash walking. Also, be prepaired to spend 30 minutes or so in the driveway making only a few feet of progress. You may want to go for a pleasant walk without the dog after these type sessions. :)

Instead of stopping, you could turn and walk a few steps in the opposite direction. Whichever you do, do the same every time. It is very important that you stop walking THE INSTANT the leash becomes tight. Don't take 2 or 3 steps then stop. Stop immediately when the leash is tight. You will know 2 or 3 steps before it gets tight so be ready.

One of our previous dogs was a puller and it took a very long time to solve the problem but we got there in the end. He pulled so badly that he would choke himself, we switched to a Halti and used a method similar to the one Bill explained. It took ages and the neighbours must have thought I had lost the plot, but it worked in the end and it was worth the effort.