The nest box is one of the main reasons that the female keeps laying eggs! Any small, dark place that the female is provided will start hormonal behavior and start her laying eggs, whether she breeds with the male or not.
You need to explain to your aunt WHY the female keeps laying eggs, as well as explain to her that it's extremely bad health-wise for her female to continually lay eggs this way, it is leeching all of the calcium from her bones and causing malnutrition. It will also eventually cause her to become egg-bound, which is 100% fatal without immediate medical intervention.
Removing the nest box is step #1. It must be done immediately or the female will never, ever stop constantly laying eggs, fertile or not. Step #2 is going to be getting her birds on a "Natural Light" schedule, meaning that they need to be able to see a window and the sunrise and sunset. They need to wake up at sunrise and be covered for sleep at sunset. This will help to calm the hormonal behavior...Step #3 is your aunt buying/ordering some fake Budgie eggs. She needs to remove ANY material from the bottom of the cage that could be mistaken for nesting material, such as any type of bedding, shredded newspaper or paper, etc. Only have the flat newspaper or cage liners in the bottom of the cage, that's it, as nesting material/bedding also causes hormonal and nesting behavior. Once the nest box is out and they are on a "Natural Light" schedule, then if the female lays an egg, it needs to be immediately removed and replaced with one of the plastic eggs, and she needs to do this with ever egg the female lays after. And she needs to just allow the female to lay the eggs in the bottom of the cage, SHE CANNOT ADD A NEST BOX BACK IN WHEN THE FEMALE LAYS THE EGGS!
If she replaces every real egg immediately with a fake plastic egg and allows them to remain on the bottom of the cage, the hen will eventually realize that they are not going to hatch, she'll get bored with them, and she'll stop laying them. The she can remove all of the plastic eggs at once, once the hen stops laying on them. She needs to freeze each real egg overnight in the freezer as soon as she pulls them, this will make them non-viable and then she can pitch them.
If these steps don't stop the hen from laying within a month or two, then she needs to separate the two birds, the plexiglass or a cage-divider (they make metal bar cage-dividers) is going to be a must, they will be able to see each other but not mate. If she does this and the hen still lays infertile eggs, then she needs to put them apart so they can't see each other anymore, as the hen is eventually going to die from being bred to death basically, or rather from laying eggs constantly.
I hope your aunt is also providing them with a high-protein pellet diet that is supplemented with a high-quality seed mix, and tons of fresh veggies and fruits daily. SHE ALSO MUST HAVE BOTH A CUTTLEBONE AND A MINERAL BLOCK IN THE CAGE. This diet and the supplements is the only thing that will keep the hen from not only becoming malnourished, but also from becoming fatally egg-bound, as a low calcium blood level is the main cause of egg-binding.