First of all, I HATE this problem. It's the most frustating one to solve. I don't know if this will work for you, but I recently learned this while reading a John Lyons book. It was suggested for horses who refuse to move forward when out on trails alone. The first time I used it, and every time since, it worked like a charm. It's incredibly simple, and I have no idea why it works so well. It's fantastic, so I don't really care. Here's what you do.
No legs. Leave them hanging at her side, but don't tap her with them. Next, one rein at a time, leave one slack and pull the other one slightly to the side until she starts to follow her nose. A few steps later, drop that rein and pull the other one sideways until she follows her nose that way. It's like a weaving drunken walk, but it gets them unstuck so you can go back to walking straight. I'm thinking the reason it works has something to do with the lack of legs. Without legs, in the horse's mind, you haven't asked for forward movement which is what they didn't want to do in the first place. I've shown this technique to a few people at my barn and was delighted to see it work instantly with them too. Give it a try. You have nothing to lose.
You just have to see your distance...you don't have to like it.