I agree, you have to go back after her. I had people call me about a 4 yr old that was rearing, striking and charging. When they asked me how I got her to stop, I replied "Oh, just go after her", and their jaws dropped. It had never occured to me that it should be that difficult for a person to go after an aggressive horse. I was just raised in a family that took on problem animals and naturally reacted that way. Be very specific, if the ears are pinned at you, throw your energy her way, if she intensifies, you intesify. Its not a matter of teaching her to tolerate you being there, but to teach her to accept it and ultimately enjoy the leadership of a person. Use enough pressure to be affective, but don't overdue it if she is willing to respond lightly.
If she takes off in a crazy run, don't worry, you are actually making progress if she swapped from fight behavior to flight behavior. Remember, even the fight side does not mean that she is a mean horse, just a very strong defensive pattern. You have to break through that pattern and discover what is causing it to be that way, be it just inexperience with people, former injury, lack of social skills, etc. After she responds in flight, she will come back to fight again, allow her to bounce around until she figures it out, this can be quick for some horses, or take quite a while for others, just keep addressing the defensive behavior until she is all out of defenses. In the end, she will actually respect you a lot more for it.
On another note, once a horse has learned that they can make progress with their aggressive behavior towards a person, that will always live in there. It actually lives in any horse, but I know that a horse that has gone to an extreme is much more likely to revert to that behavior if put back in insecure hands too soon. Make sure that her owner is ready to manage this before she goes back. If you get it under control, management would be as simple as making sure she didn't invade your space, or move your feet while leading. Good luck, and don't be afraid to look for extra help with this horse if you feel even slightly intimidated by her.