It really depends on the animal and it size but I have seen animal fasting for a year without issue.
It's hard to tell when your animal will resume feeding, but in the meantime the important is to make sure that it is well hydrated until she does and of course looking into how you can help her resume feeding faster is something to look into also.
Make sure your husbandry is optimum (not too big of an enclosure, animal feeling secure, no drop in temps etc)
Try switching the animal to a much smaller enclosure if you have not done do already does not always work but it can help them resume feeding.
Most importantly be patient and understand that their metabolism is a lot more efficient than our or any other pet you might own and of course I recommend you to read this http://jkrballstreetjournal.com/2014...-eating-again/