dehorning wont help a great deal because they butt with their foreheads, not their horns. But, sometimes it will work to knock them down a little on the social ladder. 
Here are a few other things to try, if you want to take her down a peg or two:
- join all the other goats but not her, they will have babies and she wont (this time round), most of the time the does with kids will be dominant over those without. Hopefully, one of them might knock the stuffing out of her and make her behave a little better.
- put a collar on her front left leg and her back right leg, tie a bale twine between them reasonably tight so that when she walks, she has to hobble. If she can still run quite well, tighten it. You need it so that she is quite uncoordinated. It might just slow her down enough so she doesnt beat up on the others too much. 
- take a piece of black poly pipe, when you see her beating on another goat, take the poly pipe and lay into her. I know its not nice to do, but sometimes we just have to do these things. Dont just hit her once or twice, hit her many times, hit her all over, the beauty of poly pipe is it wont bruise or do any serious damage, but it is very loud and scary. You might have to do it several times before she starts associating the punishment with her bullying behaviour.
Ultimately though, I think the underlying problem is you may not have enough space in your barn for them all to co-exist happily. Oftentimes if you can increase their space, they will all find their own little territory and get along quite happily.