Hopefully it's just the impending shed. While most cornsnakes shed once a month on average, some will occasionally shed within 2 weeks of a previous shed or take longer. It all depends upon growth rate.
If it's something else, we need some more information...when did she eat last, how often are you offering food (before and after refusal), what are the tricks you've tried, what are the temps in the viv, exactly where/how are you feeding?