The first thing that occurs to me is shedding. Is it possible that she is getting ready to shed? I know this can make them more skittish and also more likely to strike defensively as they feel more vulnerable. If that is not the case it would be helpful to know more about the enclosure (temps, layout, humidity, size, etc.). If any of those conditions are off it could easily result in a stressed, and therefore more skittish and defensive, snake. Has anything in her enclosure or care changed recently?