Lethargy and lack of appetite could be either a sign of a parasitic infection, or a response to poor husbandry ie low temps and/or lack of correct uvb lighting.

Parasites: are her stools smelly? Does she defecate in her pond?

Husbandry: What are her temps, humidity levels, and uvb light you are using? How old is the uvb bulb itself? What size is her viv?