they wont let her in the coop

[Xtineart]

The baby at the bottom of the pecking order is being prevented from getting in the coop at night by the other girls. They are sitting across the door and pecking her head if she tries to get in. Ive seen her have to spend the night sleeping in the sawdust in the run underneath after shes been bullied and stopped from getting in at night. I dont know what to do to help. Advice please