Hillaire
Chirping
what kind of chicken is she? I have bantam cochins so 12 eggs under her would be a lot. It could be that she switched nesting boxes back and forth or maybe you got a cold snap where if she left the nest too long the eggs could have stopped developing... could be a fertility issue with your roo or it could have just been a bad batch... who knows there are so many variables to account for. How good of a sitter was she