What could it be?

[Its_Julia_Chicken]

Hi my bantam Cochin is almost a year old. Just within the last month or 2 she has lost the feathers on top of her head . This is my first flock really and idk what it could be. I don't see the others picking on her that doesn't mean they don't. These are the best pictures i could get

 

[nuthatched]

Do you have a roo?

 

[Its_Julia_Chicken]

No all hens

 

[nuthatched]

No all hens

Have you treated your birds for mites?

 

[Its_Julia_Chicken]

No. How would I know if I need to and what do I use