My Female budgies Beak is part brown?

I recently bought my budgie pair a nest box and all the shedding for the nest. She has been spending a lot of time fixing her nest and she does not let her partner in. I have not witnessed them mating yet, but her beak has turned a little brown before I got the nest. It has been about a week since I have got the nest, I just want to know how I can tell if she has eggs or when she is going to have them and what are somethings I could do to help her with having the eggs, like food or her environment, etc..