You mentioned that her teeth were fine but what about her gums? Are they pink or are they a gray-ish white? How about the coloring of the inside of her ears and the coloring of her belly? If they are gray-ish white instead of pink she could be anemic. Her lack of appetite and listlesness also point to anemia. She should see a vet as anemia can be treated but left untreated could be fatal. Best wishes and good luck.