Being that your snake has never done this before, it's a little strange... Are you positive she is, in fact, a she? Mine did the exact same thing as yours and had no prior issues with refusing food, and then she laid a bunch of eggs (all infertile)! As everyone else said, monitor her weight and if it decreases too far then I would go to the vet. For now I agree with everyone else, vet sounds like they don't know what they're talking about.