She may have only been taught how to lead by someone simply snapping a lead rope on her, and pulling her along. She was probably never worked with in such a way that she really ever got used to a halter and lead.
When you get her caught each time, spend alot of time doing approach and retreats to get her used your hands touching her face and chin. Pet her in an area she likes, then move gradually closer to her head, ears, and chin...moving away before she can either pull away, or get scared enough to move away. Work on taking her halter on and off, alot as well.
As far as leading, just keep working with her. slow and gradual. If she'll accept treats, I would treat her; it takes a horse alot of trust to eat from your hand, atleast previously abused ones. I would start teaching her to disengage her hind quarters, and front end, so you have a way to keep her 'thinking' especially when you feel she is getting nervous enough to react. Pet her all over her neck as you walk, if you can, so she continues to get used to you touching her. If she walked before you got her, she may just need time to learn how to trust you most of all. She's a baby, yet, so as long as you are out there everyday handling her a little bit, she will come around. A little bit of trust goes a long way...
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."