She's hiding them in preparation to come back and sit on them later.
(forgive me if you already know what I'm about to tell you)
Eggs, even fertile ones, don't start developing into chicks the moment they're laid. They are in a state of suspended development. The development of the embryo in a fertile egg is triggered by temperature--the temperature of a hen sitting on a nest, about 99 degrees fahrenheit.
This is actually a great adaptation, because a hen could never raise a clutch of chicks if they were all different ages, since she has to get off the nest to take care of the chicks and so the remaining eggs would die. So it makes sense that there is a mechanism to make sure all the chicks hatch within a day or so of each other. There is even some research to suggest that chicks click to each other while in the shells and that helps to synchronise hatching, too.
Your hen is not broody yet, or she wouldn't be laying eggs. Broody hens don't lay eggs, which is why broodiness has been bred out of many breeds of chickens. As you can tell, Orpingtons are not a breed that's had broodiness bred out of them! It's natural behavior for the hen to lay her eggs in a clutch and hide them.
When she decides she has enough, then she may sit on them. Since each bird is an individual, I can't promise that she'll ever settle down and actually sit. You can discourage her by taking her eggs every day (especially if they're not fertile in the first place) or encourage her by leaving her eggs there.
If you want her to hatch different eggs, or you want to eat her eggs until you're sure she'll actually commit to hatching them, you can replace the eggs with fake eggs or golf balls and wait until she's sitting really tight. You'll know when she's sitting tight. They sort of flatten themselves out and get this mean look in their eyes. They'll often growl or hiss at you if you try to put your hand in there. If you pull them off the nest, they will sort of sit on the floor of the coop in a trance for a minute or two before they get up and run away. You'll know it when you see it. When she's been broody for a couple of days, wait until the dark of night and switch out her golf balls for real eggs. She'll never know the difference, and hens don't count days so she'll sit on them until they hatch.
If you want more chicks, I would say give her some golf balls and see what she does. Raising chicks with a broody is SO much easier than brooding chicks, and I try to raise my replacement hens with broody mamas whenever possible. The only difficult thing is making sure that the chicks eat chick starter instead of layer feed (and the layer hens don't eat all their chick starter). Chick starter is good for Mama hen for five or six weeks, too, since it has more protein. Do a search on BYC for a "creep feeder' and that should help you out. Best of luck!
