She will be okay. Sometimes we have to be mean moms for the better good of our children no matter the species. Yesterday I had to take one of my dogs in for a dental procedures. Broke my heart to leave her, but she is much better now. Your hen will be back to her old self in a few days and free from the desire to sit in a hot nestbox all day. Break her before it gets too hot out, and she's too depleted.