Well its easy, and you might not like the answer. Do more of what she is not good at. That's it.
You're the Boss. I think most of these kind of problems are due to people being scared to make their horse do what they tell them to do. In a way a lot of the time we teach our horses to act this way. You need to ride with confidence and determination. There really is no "big Trick" to fix this kind of behavior other then confident determined riding and lots of it. This is not a one time ride fix your horse need to learn she can and must do what you ask. Because, if she doesn't live is hard.
Think of it like this, Poor behavior gets worked, Good behavior get rest. Its that easy, when she reacts poorly life is hard, when she responds correctly there is rest/peace.
For you stay clam, when she is reacting poorly and you are fighting with her STAY CLAM, there is nothing to get worked up about. I have found that when I am having a "fight" with a horse, (like your or with other problems) when I am clam and matter a fact about it the fight is much shorter and peace is found much sooner. If I am mad and fighting then it all just gets bigger and bigger and I become part of the problem.
So all that to say, ride your horse. Put her into situations where she will reacted poorly, this will give you the opportunity to teach her how to respond correctly. For me a horse that "doesn't like" to do whatever, ride in front, ride alone, let horses pass, ride close to another horse....so on and so on. Whatever the horse doesn't like that is where that horse is ridden and we ride there until he/she is clam and responding correctly not reacting poorly. People make big big mistakes protecting and excusing their horses poor behavior (not saying this is what you are doing). Its all up to you, set your expectations high and demand that your horse live up to them.
I know this kind of horse is "not fun" to ride, "but I just want to go for a nice trail ride". Believe me I get it, But this is your horse she is yours to fix or she is your to pay someone to fix.
This is not a fun problem to have, BUT its is very fixable. Its not hard, you don't have to be a "master horse trainer" to fix this you can do it. It just takes time. good luck