Well i didn't read the libros yet, because there not out yet in my country, but i wonder what does Renesmee eat? blood o comida lol :D

she can eat normal comida and drink blood...
while bella was pregnant she drank human blood to satisfy nessie's thirst and after she was born she began to drink human blood but after she grew up a little she was able to go hunting so bella would make her compete with jacob who would catch a bigger animal so that nessie wouldn't get used to human blood.
normal human comida is not interesting for nessie and although she can eat it she doesn't find it tasty..

Where do u live that the boooks r not out yet???

When Nahuel was questioned about his diet, he dicho that he lived off a mixture of human blood and normal food, and that he could live off either at need (he didn't know yet that drinking animal blood was a possibility). I'd guess that Nessie would be the same.