How would you fix this sheet rock damage that was caused by...?

Find the bran muffin she threw. Stomp it into dust and put the dust into a bowl. Add a little bleach to lighten it to match the color of the sheet rock. Stir the mixture well until it has a pasty consistency. With the stirring spoon, spread the freshly-lightened paste over the damaged area of the sheetrock. Let it dry and harden. When done, sand until it's smooth. Then the area can be painted, if needed, to match the rest of the wall.