By math you have enough space, however your birds behaviour says otherwise. She may be getting bullied/pecked on the roosts, so take a look at that layout and see if you can adjust so they can be more spread out. Sometimes dividers on the roosts can give them a somewhat shielded space, just make sure no one can be cornered. It can be harder to integrate a single bird, they don't have any buddies and they are trying to integrate into an already formed group. I've had a couple like that, due to similar circumstances, and sometimes they kind of remain loners, staying on the edges. My space is much larger, so they have plenty of room to escape. If you can find a couple of similar aged chicks, you might get them to integrate with her separately, and then integrate that group with the others, it can sometimes make a difference. Just depends on if you want, or have the space to add. If you can expand your run and provide some places to get up an away, or to hide behind (without being cornered) that may also help. Do some observing and see if you can identify one particular bully. If that's the case then separating that one for a while can sometimes reset the pecking order and settle things down.
