Hi Heather,
Although I would have to agree with the others - that I prefer to use a prong (pinch) collar, you'll likely not be able to, as I believe that they're illegal in the UK. (Which is, incidentally, too bad, as they are a very effective and humane training tool when used correctly.) Unfortunately, I've had the same exact results that you've had with the head halters, as well as the underarm "no pull" harnesses. The head halters also made training a miserable experience for my bitch - she wanted nothing more than to get the thing off her head (wouldn't focus on me, wasn't enjoying training, didn't want the treat rewards, etc). I finally took it off of her, put the prong collar back on and she was a happy worker again!
Pulling on the lead is one of the hardest things to train away from, especially if they've been allowed to do it for any extended period of time. Likewise, especially dominant or social dogs can be nearly impossible to train away from this. I have a bitch currently living in my home who has earned her CGC certificate as well as two legs toward her AKC CD title in Obedience, and she still pulls on the lead when she gets it into her mind that she wants to meet someone. The only correct answer for her has been lots, and lots, and lots, and lots of Obedience training both in and out of a formal class environment along with a prong collar.
My best recommendation to you would be to get her into a formal obedience class and learn about the "luring method" of teaching heeling, as well as what's called "Attention", or a command called "Watch Me". This will likely help your situation immensely, but it's just so hard to teach training on a message forum.
Good luck!