Ghost eggs?

One of the chickens is obviously waiting her first egg. For the past 3 days she spent about 1 hour every morning sitting in the nest, gathering straw around and over her. The rooster is guarding her every time. But still, after 3 days no egg. I tried to feel it, there is something hard in there but I can't tell if it's an egg or a bone as I don't have too much experience. I know they usually have a hard time laying the first eggs, but is it normal to take her this long?