This is possibly the beginning of an RI (respiratory infection) to me. What are the temps (hi & low) in her cage? How long have you had her? What kind of
cage & what kind of heat? Using a thermostat? How are you measuring temps? What substrate? Humidity? Size &/or age of snake?
Sometimes bumping up the temps by a few (2-3) degrees will help a snake recover naturally from an RI, but first we want to know what the actual temps are-
in case bumping them up would result in excessive & harmful heat.
Also, have you checked her nostrils? Snakes shed their outer nostrils along with the rest of their shed...if the old skin gets stuck in their nostrils, it can also
cause the snake to make breathing noises like you describe, so it's best not to jump to the wrong conclusion.
If none of the above applies, then you might need a vet visit for the appropriate medication, but let's hope not.