You should definitely remove the nest box. I would not try to breed this pair again. Once a hen eats eggs, she usually will not stop. She doesn’t need a nest box unless she is breeding, so go ahead and remove it. You should also take steps to discourage more egg laying or she will die from laying too many eggs.
You need to do all of these things to discourage egg laying. Keep in mind that to lay eggs, she needs longer daylight, warmer weather, abundant food, and a quiet, private environment. Your goal is to reverse these conditions.
Limit her light to 8-10 hours by covering the cage early each evening
Do not give her anything to use as a nest – no bird huts or tents, no box, bowl, etc. If she decides to sit in a food bowl, remove it and replace with smaller cups.
Do not give her anything to shred such as paper or cardboard.
Rearrange the toys in the cage frequently.
Move the cage to a different place in the room. Move the cage about once a week, or whenever she shows signs of nesting – settling on the cage floor for example. This disrupts her idea of having a stable place to lay eggs and raise chicks.
If you feed a lot of fresh foods, stop offering any for a couple of weeks, and then only offer them in small amounts about 2 or 3 times a week. You can resume normal feeding later when the birds aren’t being hormonal.
If she is let out of the cage, do not let her get in any dark cozy places and don’t give her free roam.
When you handle her, limit any petting to her head and neck – do not pet her on the body. Only a bonded mate is allowed to groom the body. We can’t be a mate, so touching the body is off limits.
If there is no metal floor grate, then do not use any bedding or paper in the cage tray – leave it bare and clean it daily.
All of the above can apply to the pair, not just the hen.
Thank you for asking Lafeber,