What should I feed my turtle, and what kind of turtle is it?

I spotted a female turtle (I know it is female from past experiences) and I believe she is a painted turtle for the curvature of her shell and varying lines of orange, yellow, and red. She has two giant yellow spots on her neck. I'm not sure what to feed her, last time we bought my previous turtle its kind of food; but I am completely unsure whether I have an aquatic turtle or land turtle. The feet do have claws, and slightly webbed. She seems to prefer the water over the dirt. The only thing she has eaten is a bite of fish, a bite of watermelon, and a piece of a worm. (My last turtle enjoyed watermelon thoroughly.) I am keeping this turtle, and I want to raise it. Help?