What the others have suggested is really good ideas. Remember, try not to look aggressive in any way, because then a horse will associate catching with hunting like in the wild. Never face the horse squarely and don't walk straight toward the horse either. Move at an angle, as it is less aggressive looking.
One thing that may work, but is not always possible, is to get a horse that is in the same field as your horse, and lead that horse towards the exit of the field. Make sure they are the only two horses in the field or it won't work. Maybe if she sees she is alone, she will feel inclined to follow because horses are very sociable animals and don't like being alone.
Another thing you could maybe try is to get her into a field alone where she can't see any other horses. Go into the fields with a book or something and sit where your horse will see you. Make it look like you are busy with something interesting. If she gets closer and is focussed on you, start to fiddle with the grass or twigs or something. When you see all her attention is on you, get up slowly and walk away from her and go sit in another location abit further from her. Repeat this until it is too irrestible to stay away and finally let her see what you are busy with (a treat or some food would come handy here). Slowly slip your arms or a lead rope around her neck and then you have her.
If you just go and catch her to do work with her, that may also be disencouraging her from letting you catch her. She thinks that if you catch her she has to work, so maybe if she runs away she will get out of it. Catch her and bring her from the field to feed her or groom her every now and then, something pleasant and then let her out again. She might even want to be caught.
But ultimately, in the end it boils down to trust. Stoeka, my first pony used to run away from me in the beginning because she thought I was just another lesson kid. But eventually she learnt to trust me and now she even walks up to me in the field.
Sorry for the long post...hehe....got a little carried away. Good luck and let us know how it all goes.