Join Date: Aug 2009
Location: New South Wales, Australia
I put the stumbling down to an accident if it's only happened once.
The rest (once you rule out pain) is just a horse that doesn't respect you and needs work. Some horses are fine being left in the paddock for weeks them pulled out for a ride, others need consistent work.
You can't let horses push you around, and I imagine that's what happened. You probably started off letting her get away with something little, like going into your space or pulling on the reins, stopping when she wants. Each time she refuses to go and you don't make her you're training her not to go. Once she's won once she'll try it again and again and get worse and worse.
On here you'll notice lots of people say "groundwork" and the reason is because if your horse doesn't respect you on the ground they likely won't respect you in the saddle. If you can work on that until she leads on a loose rope, backs and yields to pressure, lunges small circles then hopefully you'll start having "little wins" that will build on each other.
A harsher bit is not the answer. A horse doesn't naturally stop or turn with a bit, those responses are trained so if your horse isn't responding chances are it's their training that needs work. Unless you have to - keep out of the horse's mouth, that agitates them and escalates the situation. To get her moving forward you should need no mouth and all leg, if she goes to turn use one rein, releasing when she's facing the right way. Even if she's acting up always release when you get what you want, don't hold on because you "know" she's going to do it again.
I don't know what level of riding/handling you are, and it's probably best if you can get a trainer out for a few sessions to help you find safe ways to work on these problems.