Pomeranian with food aggression?

Ok so we have this pomeranian that we bought at Petland 6 years ago. Basically she is very very obsessed to food and she always has been. She begs constantly, and eats everything. If she gets her mouth on something she is not supposed to have, she will bite and growl when you try to take it away. She also sits by my grandma when she is eating and paws at her leg constantly. Im sure it doesnt help that my grandmother deicdes to let her finish off her dinner sometimes... does this mean she was like the runt of the litter or something? Why would a dog be like this when you buy them? She is also inbred if that makes a difference...