Basically she flipped out as soon as she felt any pressure. Ended up almost breaking one of her legs. Then she shut down completely. Apparently her eyes glazed over, she dropped her head down to the ground, and wouldn't move at all.
Second attempt about a week later was about the same. The girl had a farrier out (who has experience with this sort of thing) and the filly did the same thing, although I believe she shut down faster this time. They left the halter on her in hopes that she would become used to it and it wouldn't cause such a problem.
At this point the filly has lost all of her friendlieness/curiousity and really wants nothing to do with anyone. Friend asked for help so I went out. What I suggested (and we did) is taking it ultra ultra slow. We went out with some oats and started working on her letting us touch her body. Then we worked up to touching her face and then the halter. Towards the end I got her to start giving her head when I put a small amount of pressure on the halter (she started to pull back at first, but she calmed down). At last I got her to take a step with pressure. I was also calling her to come to me and rewarding with oats/scratches, hoping that it will help in the future.
Soo.... Does anyone have any suggestions? I don't know if what I did has any chance of working in the long run. I've never had a foal so I've never had to halter train and I don't want to cause more problems for this horse. My friend is out of ideas, her other foals have all been easy as pie to train for everything, so she's stumped.