Has your bird bathed in the last few days? Do you have any idea what the humidity level is in your house? how long do you think she has had the appearance of an egg?
I'm assuming this is the bird's first nesting...and possibly your first encounter with a nesting hen.....young hens/first timers should be watched for possible complications...they might also require calcium supplementation, especially if you are not feeding calcium rich fresh foods...and if your home is too dry, it can affect her ability to expel the egg and could necessitate a veterinarian's intervention.....
If she doesn't pass the egg by tomorrow morning, you might be wise to call & discuss the situation with your vet because egg binding is a life threatening situation.....
Good luck.....