2yr old chicken behavour

[k1tchener]

i have 5 chickens and one off them has just started not going in to the coop at night. She sits under a bush and I have to lift her in. Any ideas why?

 

[Stiggy]

is she acting normal during the day? is she a good weight? and does she have clear and bright eyes? also have you changed anything in the coop? its possible that she is being bullied and that the others arnt letting her into the coop