How do you know if your parakeet's egg is fertile?
You can check the fertility of an egg by going into a bathroom with a flashlight and "candling" the egg. If it is mostly dark with a little bit of a clear section it is fertile. If the whole egg is glowing from the light, it is likely empty. If you are still unsure, a fool-proof way to check is if the egg floats in water, it is infertile.
If it is infertile, there is no harm in leaving the egg there until she leaves it alone. If you are not wanting to add to your budgie family and it is fertile, before removing the egg (as removing it may simply make her want to have another clutch) find a replacement egg. These can be found at petstores. They are fakies and she can sit on it until she feels it's no good and leave it. Then you can remove it and no harm is done.
The Full-Proof Way
If your egg is floating like this one, then its infertile.