That lower photo says all we need to know about Ethel. I have a friend like her. Stubborn, set in her ways, and you can't change her mind, no matter how hard you try.
My friend may be a hopeless cause, but there may be hope for Ethel. The key to changing a chicken's obsession is to try to make it as unpleasant as possible or remove the attraction entirely.
Unfortunately, you can't block off the nests when other hens need to lay, so you are going to need to play hall monitor for a little while until Ethel can be convinced that her obsession is ruining her life.
I have a Buff Orpington named Edith that bears an uncanny resemblance to Ethel. Edith had a bad habit of terrorizing the other hens as they tried to come in to the coop to roost. I kept a fly swatter handy, and each time Edith would launch her terrorist act, I would swat her, just a friendly tap, on her butt. It worked. Beyond my wildest expectations. It nipped the behavior in the bud short term, and over the long term, applying it when I saw her go into her act, it has all but changed the behavior except for very brief spurts where she just can't seem to help herself and she regresses.
Stand guard at the nest, fly swatter at the ready, and when Ethel jumps up to enter the nest to bother the occupant, give her one across the beam.
Let me know how it goes. Good luck.