Agreed Mincie, and make sure its shelterd and in the sun!
Have you got a REALLY good filter in the tank?
A few food ideas for you.....
Feed her variety. Chopped up ox/chicken or lamb heart (NO fat), any turtle food from pet shop you can get her to eat, insects, worms, snails, bits of courgette, banana, pumpkin, peas, frilly lettuce, water lilly pads and other water plants, boiled eggs and egg shells, purina 1 cat biscuits, dried fish (Purranas sold as cat food in supermarket), raw fish, hot house turtle food, blood worms, float a cuttle fish/bone (Sold as bird food at supermarket) in the water.... When introducing new food you can leave her about 4 days with no food and then feed her the new food when she's really hungry. Good luck!