Oh, good! Another Oregonian on the board! Welcome.
A whole lot more info needed. Is she spooky anyplace else? Do you arena ride or trails only? Recent change of tack? How old is she? Gained or lost weight (possible change in saddle fit)? How are her teeth? How long have you had her? Do you go out with other riders or alone?
So many possibilites. It's odd that she has been fine and all of a sudden is trying to bolt. If you could give us a bit more information we would be better able to offer suggestions.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger