She is definitely a feral chicken, but I'm going to guess that she has a mix in her as well. Her body shape is not as defined as it should be, but her comb is identical to one of my jungle fowl, and so is her behavior. If she has a high pitched voice then you can be sure she is a feral hen mix ( they are the only birds in my flock with a high pitched voice,) although I'm already sure due to your photos. Feral chickens can look a bit different depending on location too.
Here is some photos of feral hens off the web for you to compare:


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Here are two of my feral hens



, I will try to get a photo of them from the front today. (My pics)
I'm thinking she is a mixed breed because of her pink legs and darker coloration. I would place high bets on a Welsummer X feral chicken mix, but she might be pure feral, I'm not too sure.
All in all, her behavior is normal for this breed. I know she may peck her coop mate, but I'm guessing she is secretly happy to have another hen around. Like I had said before - my feral hen will peck anyone who dares get too close, but I know she still loves all her sisters. If you are worried about your new hen feeling lonely, I wold get her a flockmate of a calmer breed to hang out with, especially if your feral hen doesn't come to like your new girl.
You can temporarily separate them, to let them get used to each other through a fence for a few days.
best of luck!
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