Killer broody?

I found a broken-necked Coucou de France hen in the same nest-box as a RIR. This bird has no eggs of her own but she's been broody for days and covering eggs laid by other birds. I've been taking them off her as the box is not in a good position for brooding. I've tried moving her with the eggs to the woodshed with our other broody hens but she won't have it and abandons them.

Would the Coucou have been killed for its egg? Or would it have been killed for disturbing the broody hen when laying it?
I found a fresh-laid egg under the RIR.