Is there a pond, or lake where you live that the turtle could have come from? If there is your best bet is to put it back. If not, maybe someone has a pond that she escaped from, or they just got tired and "put her out". Sad, in any case. Try some live blood worms, or dig up a worm in your garden. Also, some water plants that you would put in a pond like duckweed. If she comes from a nearby pond, she would not know about turtle food, and would be eating water plants, and little bugs that are in the pond. Or you could try a small goldfish. This is not a good diet, but it is a start if you want to make her eat. When I first got my rescue slider, she would eat nothing but dried shrimp.