Sounds like you have a bit of a project on your hands. I would start out with making a list of all the specific problems (ex: tries to nip me when my back is turned, balks under saddle etc). Then, next to them, write how you are going to fix it. Do research online and ask horse friends to find methods that work for you if you can't afford a trainer. That should get you started. When you discipline, a good rule of thumb is to do it within 1 second of the behavior, and try to prevent it from even happening. As a starting tip, when you walk into her pen and she shoves you around, take a lead rope with you. Swing it in front of you like a helicopter blade if she tries to run into you. The lead horse moves the lesser horse around, you don't dodge for her.
"The trouble with the world is that the stupid are certain and the intelligent are full of doubt"