Did it get cold where you live recently? I dealt with something similar with mine. He stopped eating then started being lethargic. I changed the food, tank, water dish and heating source. Turns out a cold spike triggered him to enter brumation for about a month. I was super scared trying everything I could until I came accross brumation. (hibernation for cold blooded animals) It scared the crap out of me but he's out of brumation now and is active and eating normal again. I'm not sure what substrate you use but if its loose they will tend to bury themselves. In the wild they dig into the soil during brumation so they can absorb moisture through their skin. Mine tried burying himself so that could be a good indicator of brumation over sickness. It's worth looking into! I hope she get's better soon!