So here's my solution, which is a bit of a time sink but if you're around enough during the day to make it happen...
Try and figure out the problem bird's laying schedule (if you know the approximate time she laid on one day, you can usually guess when it'll be the next day). When she goes into the coop and sits down to lay, pick her up and put her in the nest box, and block off the box entrance. I use my arms to bar them in but you could use something else if needed. Wait until the bird starts exploring and considering the nest box for possible use, then slowly back off and see if she stays in there. If she doesn't seem inclined to leave, you can leave her alone and check back later to see if she laid in there.
An extreme version of this would be to lock the bird into the nest box when she is supposed to lay, but that still requires that you have some idea of her schedule so she doesn't stay locked up for an extended period of time.