Clarification: This cage was set up in the coop that held 3 of the four broody hopefuls. The Araucana was from the other coop, and I put her in there because her home coop is too small. It seemed to work fine since it was only 3 days in all but one case (the barnyard mix was extra stubborn).
I'd candle that egg at about 5 days to see if it is developing. You should be able to see veining and darkening by then. If it is fertile and you have the room for a chick, let her hatch it. I would probably have given her 3 or 4 to be sure she got a baby, but that ship sailed 2 days ago...
This is my setup for Snowball (English Orpington).
The cage below her is where my 14 week olds go to hide out from the bigger birds. I have her on 2x4's with a pad below them to catch the droppings so she doesn't poop on the babies heads. I sure hope this works. This is her second...
The coop has very large windows, and the cage will be in line with the windows. It is actually more comfortable than it is in the yard in there. I've been surprised how comfortable it is. that is a good thought though.
Does this work if it is in the coop with the other hens? I have an 8x8 coop with a good spot for a raised dog cage, but I don't have a place cool enough outside for it (it is nearly 100 here today).