My horse won't let me catch her in the field?

She's playing a game with you. It has nothing to do with how nice you are or aren't to her. The best way to deal with this is to get her into a small paddock and work on walking her down. You will keep her moving, even when she wants to stop, and finally when she stops and looks at you, you can turn around and walk away. Then walk back up to her. Scratch her withers and walk away again. Repeat this. Then when she's out in the big paddock, do the same thing. Don't always catch her and bring her in to ride her, but catch her up, scratch her withers and turn her loose. You can also give her a treat after you catch her, then turn her loose.