[Chicken star]

I have a silkie hen sat on about 7 eggs and I have just left it completely up to her she chose the eggs (Very good fertility chance as all my hens are running with a cockerel) She was sat in a brooding box so after about 2 weeks I locked her in to keep the others from disturbing her.
Anyway today, day 16, I noticed that when she stood up for food one of the eggs was cracked and was completely empty no liquid, chick or anything. I decided to leave it there as she was getting stressed when I went near the eggs.
When I went down again at night she had chucked the egg out. I carried on feeding the rest before getting it out and then when I went to get it she had sat on it again and wouldn't let me get it!!!
I've had broody hens before but have never seen this type of behaviour. Has anyone got any explanations or seen it before?
Thanks