Help?

[Maple Cake]

I'm new here.
I own a mixed flock of bigger sized hen breeds.
One of my jersey giants went bald on her underside (it looks red) and now she's balding on her face.
Is this some sort of infection? Mites? Bullying from other hens? It's happend just recently and none of the other flock members show similar issues.
Do I need to isolate her from the flock? Please help.

 

[DLA]

Could be some kind of pest. Please inspect her very closely and see if you can spot anything and check if any eggs on feather shafts. Can you post some close up pictures and we can help you look.

 

[Maple Cake]

Could be some kind of pest. Please inspect her very closely and see if you can spot anything and check if any eggs on feather shafts. Can you post some close up pictures and we can help you look.

Sorry if they are not the best, she kept running from me and looping under a bush in their pen. Got the best takes I could.

 

[DLA]

It's hard to tell from the pictures if there are any pests. It looks like feather pulling. Her red bum is just going to make it worse, you could try some blue kote to hide the red and help it heal. If you can watch them and see who is being aggressive and when/how it's occurring. Do they all have enough room and places to get away from each other, how many chickens do you have, how big of a coop/run do you have? Also diet can sometimes be a factor, what do you feed them?