Thank you vfem,
I do not have any roosters, so I do not have any fertilized eggs. She indeed started the behavior after about 15 eggs. I have been giving her food and water to make sure she gets all the nutritions needed. Today was the first time that she mingled with the other three girls, but one of them now started to peck her. She went straight back into her nest. The other two came into her nest and encouraged her to follow them, but she stayed in her nest.
How long do you think this will last? Should I provide her with a wooden egg (I read that would help)? Sorry for my ignorance as Im a first time chicken owner.