It sounds like she is being disobedient or doesn't understand what you are asking of her. You need to gain her respect. I train thoroughbreds and rescues and try to use the simplest of methods to start off with.
How is she with groundwork? If you are having trouble there, that would be a could place to start.
If you are having trouble with one gait under saddle, do not move on to the next until she is truly listening to you. So I suggest going back to the walk. This will give you a chance to really figure out what is causing her to be difficult. And remember to pay close attention to body language, that will tell you a lot
For this kind of issue I like to use parelli. I've posted a link to an article on their website. It talks about the different phases you should go through when trying to get your horse to go. It is very simple, but takes some patience on your part Correcting Horse Balking Behavior | Parelli | Parelli