Like many people have already said, I definitely wouldn't have hit her for backing away.
As for the catching thing, my horse used to be really bad to catch, we would spend hours (literally.. the longest was 4.5 hours once) trying to catch him. The way we fixed it was going slow and not getting mad. We'd start by just throwing the lead rope over his neck, if he ran off, fine, try again. Then leading him around with the lead rope around his neck.
Once we could finally got a halter on, he got a treat, but only once the halter was on. We would lead him around a few feet, then take it off and give him another, then let him go, just so he didnt associate being caught with hard work every time. I wanted to show him that just because im haltering him doesnt mean we're going to work, maybe we're just going to hang out or go for a walk or something. Maybe I just miss the way it looks on his face. Who knows! So that's what I did, put it on, take it off. Some days I would go to the barn just to do that, and then leave. Eventually he was like hm, okay, this isnt so bad.
Also never ever give up. Even if it takes you all day and a night. If you give up and leave the pasture without her, it'll be horse wins, you loose, and she'll know that she just has to run off long enough and eventually you'll give up and leave her alone. Never give up!
Now rummy is a dream to catch. He gets one cookie once the hater is on, and one when its off. This prevents him from running away like a mad man the second the halter is off. This is the only time he gets treats. Now he associates being haltered with getting cookies, which makes him very willing and polite. Its so frustrating, trust me I know. But she'll come along with the catching. Also when you approach, kind of meander over in a casual zig zag instead of making a bee line straight for them. After about 3 tries of him walking or running off I would drive him away as if it was my idea and I didnt want him. Eventually they get tired of the nonsense and surrender :)