so my hen is still broody,

i was scared she would not back out of it becuz this is her first time. but she keeps getting of her nest. i have the coop door shut so the big hens wont mess with her, and she has water and food, but when the big hens are in, like in the morning and at night. they are always pecking her until she gets off. im afraid to give her fertile eggs. this morning i went to let them out and she was off the nest, even though there were no other hens on there, and the eggs were cold. what should i do?