Chicken won't defend herself

[Lilly chan]

I have a chicken I added to the flock and thought the pecking order had been sorted out by now. It's been more than 3 months and the only thing I still see is one of the chickens chases away the new one when food is involved. The newer chicken still seems to get enough food though cause they have our entire backyard to be in all day and it's a big backyard.

My problem is that a couple of times now I have seen the same chicken that chases her now pecking the newer chicken's neck. And the newer chicken just squats and takes it! When we first integrated she would run away but why wouldn't she now? I don't see any injuries on her except a small place on her comb that is already scabbed. I simply removed the bully chicken both times and placed her in the coop (she could technically get out but it took her several minutes before she actually did-it astounds me how slow these chickens can be!). Why wouldn't my newer chicken run away?

 

[Wyorp Rock]

This is the way of chickens. Behavior sounds pretty normal to me.
Some are more timid and submissive than others.