Hen only shows up for breakfast and dinner why?

Our Chickens are Free range and in the coop at night. A few days ago we thought we lost one of the girls because she was not in the coop for the night. We searched but didn't find her. She showed up the next morning for breakfast and then was gone until dinner when she showed up again. Once again she is not in the coop for the night. Next morning she is back to eat and again at dinner then gone until morning again. We can't find her during the day or night. Do you think she is sitting on eggs somewhere?
Thanks
Wendy