One of my chickens is sleeping/closing her eyes a lot in the day!

[MychickensandI]

My 5 month old Blacktail has started to close her eyes/sleep a lot during the day. This is totally not normal for her. She is still eating, drinking, and pruning and is alert when awake.
Anyone know what could be causing her to do this and should I be looking out for any symptoms?

The other chickens are absolutly normal.

 

[Cupcake1243]

Have you been feeding her anything differently recently??

 

[MychickensandI]

Have you been feeding her anything differently recently??

Not that Im aware of but maybe one of my children have without me knowing?