Here's my two cents... if you can afford to, I would possibly think about finding a reputable natural horsemanship trainer in your area (if there is a good one) and see if they can come out and get into her head... someone needs to nail down the true cause of her behavior (i.e., scared, bratty, etc.)
before her behavior issues can be tackled.
At the least, if they can give you some direction on how to work with her to not only discipline her when she acts out (if indeed, she's just being bratty) but find ways to
discourage her to not want to act that way in the first place... otherwise, I'm afraid you'll just end up in a pissing contest with her—she kicks, you discipline her, she kicks again, you discipline her again—she needs to be diffused of her behavior, if it is ever going to change... and you don't want her learning to associate a negative response with you, or it could make things worse between you...
For example—and I'm
not saying this is the best thing to try, just using it to make a point—some people put a kick chain on a horse's back ankles. When the horse kicks, they punish themselves—it doesn't come from you. And it doesn't take long before they'll not want to do it (although I'm sure there are exceptions!). So, the right trainer should be able to suggest some things that work in the same manner, perhaps...
I'd just hate to see her get worse, and either you or someone else get hurt in the process... I'm confident she can be turned around, but you want to do all the right things from the get-go, as it's a serious situation.
JMO, for what it's worth!