when hens are close to breeding they will show some sort of interest in a nest box (do not rely on their cere being dark brown when they are ready to breed as this is not always the case), try fixing a piece of very thin wood over the nest box hole, with a smaller hole drilled in it, about her head size- hens curiosity will get the better of her as she cant really resist a hole to peer into, then if she "wants in " she will gnaw away until she can actually fit in (some parrots and budgies do not like the hole size therefore problem hens can create their own size hole that they are comfortable with, others will enlarge the nest box hole) - in the old days (many moons ago, and some breeders today) you would put a log or large timber box hanging in an aviary with many holes in it, then hens get exited by this, maybe try half filling the nest box with pine shavings - while dhe removes the shavings she may be more receptive to breeding
let me state that I have never had a problem in 25 years with hens wanting to breed , generally it may be fertility that may let me down (usually a particularly good hen that I reall want to have eggs)
also it has been noted by other breeders that leaving the hen with the nest box by herself for at least three days, so that she knows that it is hers, then introducing the male helps