I think your horse is anticipating the spurs. I worked with a horse that someone had cinced up hard and fast and it took me 3 months to get her to stop anticipating the pain. If you have ruled out pain with her teeth, tack, ect....then it is an attitude problem. Stsrt her out on a very short ride outside the arena....as soon as she starts to act up, calm her down, and go back.....slowly increase the distance that you ride. Pretty soon she will relize that the spurs are not their and that it is anot acceptable to buck or act 'stupid'
And over all please be safe. If you do not feel comfortable fighting it out with her, get someone who is.