I guess that the greyhound is snarly about food because for most of her life she's been kept hungry and desparate for the stuff. What you need her to understand is that she will be fed and that food isn't going to be a problem anymore. I'd suggest keeping the two dogs separate during feeding, at least until she calms down a bit. It might even help if you left the room whilst she was feeding.
Another thing that might help could be to give regular (healthy) snacks with a happy positive vibe, "Here you go! Have a biscuit!". The point here is to associate eating with a positive vibe, whilst at the same time not giving enough 'food' for her to get defensive about.