^^^^^ Agree with all of this
This is not how it works. ALL of her confidence comes from you. You have to be the leader that she has confidence in.
This has absolutely nothing to do with what you need to do to train her to do anything, including go forward when she is told to go forward.
I've trained horses for 55 years and I have never seen letting a horse call the shots and determine what they will do that ever resulted in the horse 'trusting' the person that was letting the horse call the shots. This never results in a confident horse like you want. Trust comes from the rider / handler having confidence and earning the horse's respect.
We simply call this 'having the horse train the rider'! This horse has trained you where to let her stop. She has trained you to get off. She has trained you to do what she wants in order to avoid her tantrums and fits. This is no different than the spoiled toddler throwing a fit to get a piece of candy and then having the person in charge run and get the candy so the toddler will stop throwing the tantrum. Same thing exactly.
The 'fix' is really simple. You get after her butt and make her go forward when you want her to go forward. You need to do this at home first before you head out on the trail or road. Good forward impulsion when you ask for it is the single most important thing you need to teach every horse. Until you have taught that going forward is not optional, you are only playing a game where you wait and see when or where your horse will refuse to do what you want it to do. All obedience is optional in the horse's mind until you have taught it to go forward when you ask it to.
Personally, I will take the long ends of a pair of harness leather western reins and 'over and under' the horse very quickly and I have yet to find one that won't go forward. I never use a whip because you just end up with a horse that ducks around and changes directions moving away from the whip instead of going forward.
If a horse horse does duck around, ALWAYS turn it back quickly and decisively to direction it turned from, ALWAYS. If a horse spins or ducks around to the left, turn it back quickly to the right. Do not wait a second. Pull it around harshly and drive it forward. Better yet, spank its butt with an over and under (back and forth - right -- left -- right -- left) and it will go forward. If you do not have the seat or confidence to drive this horse forward, then get someone else to ride it for a ride or two.
It will be much easier though, if you work at the barn teaching it to move forward quickly and with good impulsion first. Never 'baby' a horse that is wanting to stop -- NEVER.
Read through this entire thread. It goes to the core of your problem.
http://www.horseforum.com/horse-training/just-how-important-establishing-forward-impulsion-501186/