This might work. When I want hens to lay elsewhere I leave an egg in a nest. An egg in the nest will draw hens to lay there. But you need to make sure the nest isn't too close to the broody or she might get on that nest by mistake after having taken a break. A better solution is to fence in the nest so other hens can not get to it (not always possible). A combination of the two works also. Block the broody in when the other hens are laying; after a few days they will have chosen another nest to lay in, Leave a dummy egg in that nest so the layers continue to use that box and then the broody's box can be left unblocked.