Chicken(s) roosting ON nesting box

[Lifewithchicks]

Is she completely recovered from her illness?
She may not have worked her way back into the pecking order so might be being excluded from the roosts by the other birds?
Knowing how many birds total, dimensions and pics of coop and roosts, might give clues for solutions.

She is completely over her illness. Now her closest companion isn’t acting herself so I had her inside last night. So there were only 2 chickens on the roost last night. The pecking order thing could be it, but why wouldn’t she choose one of the other 2 bars?

We have 4 hens - 2 barred rocks and 2 buff Orpingtons. I can ask my husband about exact measurements, but the coop is built for 8 birds. There are 2 tall parallel bars and 1 lower bar.