How to say "no" when someone asks to share food?

You need to act ignorantly bliss untill she gets the picture. So heres how it goes, you can see her doing her normal act to guilt you out of food pretend (staring of some kind) just don't see her.. Even if you can tell she knows you know and when she asks a dumb selfish question non-chalantly say "Naw thats okay I'm gunna eat all mine" and she may look sad for a bit longer but she will get the picture and move on the next victim:) She needs to be left feeling a little socially awkward or she will never learn her manners.