Is my chicken ok??

Just noticed this morning that 1 of my chooks is bald around 1 eye.  She is the only one that I can't handle unless she is sleepy so will have a look at her tonight when I get in from work but was just wondering if anyone on her has any ideas why she is bald around 1 eye.

Thanks

They were wormed about 1 month ago (not really sure how ofter I should do this??).

I have just checked her over and the area is bald and slightly swollen but her actual eye is very clear and healthy.  I can't see any lice and I checked the house at the weekend and couldn't see any mites but I believe they are very hard to see so not completely sure.