
The headcollar needs to be introduced gradually, not just put on for walks - the sort of reaction she's seen is common in that situation. It is a totally unnatural thing for dogs to wear, so it has to be made into a really good thing for them.
That has to start at home - reward the dog just for looking at the headcollar, or touching it. Then holding it up, reward the dog through the nose loop. Then draw back a little, so she has to poke her nose in a little to get the treat. Then further back so her whole nose is in. Then rest it on the bridge of her muzzle for just a split second before rewarding. Then a second, then two, so on and so forth, building up the time. When she's happy with it resting there, do the buckle up for a second, undo, remove, reward. And then build the time up with it buckled.
Every step above has to be done repeatedly until the dog is totally comfortable with it. Once she's happy with wearing it like that, it can be left on for increasing amounts of time indoors, to coincide with good events - pop it on before her meals, or before a play in the garden. When she's happy wearing it for all that, she can go for a short walk with it on - ideally without the lead clipped on to start with, so she's not getting the tension on it to begin with.
It's all about patience - she's really not happy with it now so it's going to take a while and I would change type, too. Haltis are IMO the worst headcollars out there - they ride up, they are not comfortable. Gentle Leaders are better, Dogmatics are ok depending on the dog (lot of webbing under the jaw which some find uncomfortable). My personal favourites are these from Houndstuff:
http://www.houndstuff.co.uk/headcollars.htmlBit of a fiddle to get on but they are the best I've tried and I've seen both the best response for training and the best reaction just to wearing them of the ones I've tried (the above types and canny collar also).