New hen isolating herself from others

I got a new-to-me pair of what I think are americaunas (that's another thread for another day, previous owners said they were auracondas lol). They both seemed very healthy and don't have any skin issues or anything. I am having a problem with the hen, who is approximately 4 years old. The first day, she was in with my flock, she did great. The next morning, she was just OK. She ate a bit and then started to sit in one of the nesting boxes. I thought that she would maybe lay me an egg, but she never came out, she just wanted to stay in there for hours. I noticed that she had some blood on her rear tail feathers, near her vent, but I can't see where it could have come from because her vent looks clean and normal. So I am thinking that perhaps one of the other hens were initiating the pecking order and picked a blood feather? Her feathers seem a little roughed up since we first got her, and it's not uncommon for my Wyandottes to to peck feather tails. That was yesterday- today, there is no new blood. I'm not sure that she is sick or anything, but she isn't acting like what a normal, healthy hen should be acting. This morning she did come out into the run to get some fresh air, and I thought maybe she was coming out of it, but then a few hours later, I found her between the nesting box and the wall. I don't think she is eggbound because I can't feel anything where her uterus is. At age 4, would she be laying very many eggs anyway?
Sorry to ramble on, I just felt it would be best to be as detailed as possible. I'm not sure what could be wrong with her, everything seems healthy. Eyes are clear, poos look normal, no mites or bugs in her skin.. Could she just be depressed or something?

 

Thank you! I will pen them up separately so that they can't bully her. The rooster is getting along just fine, I think that the girls are just being that-girls. She is extremely friendly, so I think that my girls are just harder on other new girls and may have been causing her to be a bit depressed about it.