Bluebird has only laid one egg and doesn't sit on it Do I remove the one egg?

Bluebird will need a rooster with her to make her eggs fertile. If there is no rooster her eggs will never hatch so remove and enjoy boiled, scrambled, fried etc. Do not leave the eggs in the nest too long or she might accidentally break them and eventually they will go bad.

If Bluebird has a rooster friend her eggs are likely to be fertile. Chickens can lay only one egg per day, but they like all their eggs to hatch at once. They manage this by laying one per day until they have a number of eggs (called a clutch). Once they think there are enough (up to about 12) they will start to sit. This means that they keep the eggs at the correct temperature and humidity to start the development of the chicken embryos. All the eggs will start together so they will all hatch together. Once they start to sit (or brood) on the eggs the hen will leave the nest only for quick food and water trips. Some very dedicated hens will need encouragement to do this or they will almost starve themselves.

Some hens are not very interested in becoming a mother and they will not sit on eggs at all or will start to sit and then lose interest. With a hen like this you are better off collecting her eggs and either hatching them in an incubator or under a more dedicated mother.

If you do not want to hatch chickens just keep collecting Bluebird's eggs as she lays them and use them in the kitchen even if they are fertile. Remember that the embyro will not start to develop in a fertile egg until you keep it in the right conditions, so just store them in the fridge as normal and they will be fine to use.