"I eat an apple and she eats bread."
Translation:Io mangio una mela e lei mangia pane.
In English, "bread" is a mass noun. You can't specify a quantity without adding a unit - for example, you can say "a loaf of bread" or "two pieces of bread," but NOT "a bread" or "two breads."
"She eats the bread" would usually mean she is eating all the bread, although there is at least one exception that probably isn't pertinent here.