One of my hens is acting much differen than the other 3

[hiltonmagic20]

I have 4 Rhode Island Red hens and three of them stay with each other while they are in the their run, as well when I let them run free in the backyard, but one stays by herself. She is still eating and drinking, but she is keeping to herself and not following the other 3 hens throughout the day. She is also moving around slower than the others. Today I shook some seeds in a cup which made the other 3 come running, but the one other hen didn't come over and kept grazing in the backyard. She has also been doing a lot of sitting around while the others are off scratching for food. Her eyes and comb look normal, she isn't having trouble perching or breathing. She is also sleeping further away from the other 3 hens at night. This behavior has been going on the last week or so. I'm thinking she is just the outcast hen, but I'm not sure. Does anyone have any idea what could be going on with her?

 

[collingwood]

How long ago was she introduced to the flock?

 

[hiltonmagic20]

She grew up with them as chicks. The 4 of them used to hang out together, but now one of them doesn't seem to be with the other 3.

 

[collingwood]

She may be getting bullied!