Lots of horses do that, its just a way of testing you. I have heard of using a bag of oats on a horse in replacement of a rider. I have never used that method though. If it were me I would lunge her until she starts licking her lips and putting her head down (signs that she wants to be wiht you) then get on her and ride her. Make sure to put her away on a good note. Don't let her get away with it. When does she buck? Like are you leaving the barn? Her herd?
Lounging is always a good way to work on the ground. As long as you focus on the horse paying attention to you and listening to what you tell her to do. If you are just running her to run it's actually counter productive. Make her focus on you and when you tell her to go faster, slow down, or change direction.
You could also do desensitizing with her and get her to accept new, scary things. By doing this she will trust you more.
Also, you can stand facing her and get her to back up. Start by lightly shaking the lead rope, and gradually shake it more until she takes a step back. The instant she does stop! Back her a few more times and then ask her to come to you. Repeat the exercise 2-3 times. This teaches her that you are the dominant and she must listen to you.
You can also get her to give to pressure. Stand next to her and apply light pressure (such as a gentle push) to try to get her to move sideways AWAY from you. She'll more than likely push against you. Keep increasing the pressure until she moves. It may become a battle to see who is more stubborn, but don't back down. If you do it teaches her that she doesn't have to listen to you because you will back down. When she does move stop pushing her immediately. This is her reward. Be sure to do this on both sides and in different areas: shoulder, side, hindquarters, ect. This will also teach her that you are the dominant and that she moves out of your space.
You can always just take your horse for a walk. It's a fun way to spend time together, and she has to listen to you. She'll get more out of it if you turn, stop, and back a lot.