The aggressive mare may have been taken down off the top a notch, but she does not see YOU as above her. you are below. If you can move the horses, any of the horses, that alone shows your dominance to start with. even herding the other horses around a bit show them that when you walk in, YOU are the herd leader.
If you must feed them out in that open situation, can you put down a few piles of hay around the area to keep the other horses off of you for a bit? Shouldn't they all be fed at the same time, with spread out piles (always ONE more pile than horses so that it eases the pressure as the dominant horse pushes the lessers off their pile)
As to a whip, I find a lunge whip too hard to manuever quickly and in close quarters. I use either a dressage whip, or a buggy whip. If you vibrate it rapidly in the air toward the animal, it makes a very intimidating noise.
The instant that mare starts to approach you, and I don't mean even to be nasty, but just to approach you uninvited, you turn towardx her, pin YOUR ears and start vibrating that stick out toward her. you stop her advancing. She is NEVER to approach you without being invited. If she tries to go around, you "chase" her a bit until she turns away, then you ease off. Don't chase at her if she is moving away from you, but if she turns in preperation to "fire", then whir that whip fast and furious, and if you can smack her without being kicked, you lay it on her with all your might.
You get her to stand way off from you and ask for permission to come in. If you think you can deal with it, walk up and pet her on the nose and then walk away and leave her, but keep reminding her, she NEVER approaches ONE step toward you (I mean closer than about 20 feet), that you don't warn her off.
You have to develp eyes int he back of your head and cut off the very small ways that she tries to get past your "line". If you have to hit her, do it with total committment.
If your mare runs off, don't worry too much. She will get used to it, and your moving her and the others is another demonstration of your dominance. Horses are usually pretty good at sorting out which horse you are "after" , so I bet she'll get over it. Heck , she might come to see you as her "protector" once she has confidence you can move off the "bully" mare.