I had this problem with my hen. It was the first time I had a broody hen so I did not have experience. She got off the eggs and they never developed into chicks. On day 30 I went to the feed store and got some day old chicks and slipped them under her. She was a good mother hen to the day old chicks.The eggs should be fine, but you are going to have to do something so this does not keep happening.. She "probably" got off the nest to eat etc and when she came back another hen was on her nest so she took the other. "I" would remove her eggs and put fake eggs under her----then move her in a couple days--at night, then if she accepts the move---set her with a nice nest of fresh layed fertile eggs. Good Luck!!