It could last a year, it's a mature female over 1100 grams if your husbandry checks out there is really nothing to do except being patient.

I would also cancel the vet appointment, it will be a waste of time and money and depending on how honest the vet is he could very well take you on a ride (from recommending X-rays to blood sample etc)

This is what they do just remember that snakes metabolism cannot be compared to mammals, I know it is frustrating however so long the weight is maintained and the animal is well hydrated there is nothing to worry about.