A Real Shock!

[Catherine]

Allison may be young, but she wouldn't lay an egg until she was old enough.  This first egg might not be fertile. Many of the eggs are not. She will sit on it for awhile. If it is not developing a chick she will give up. If the egg breaks it will be because it dried up, which happens if the egg does not have a growing chick.

If she stays on it and it hatches it will be so cute. Find out from someone locally who breeds birds what you need to feed the chick.

You should be able to get her a nest  box for next time. I know a lot of pet stores carry nest boxes that work for Budgies.

Good luck to you and Allison. She sounds like she has the proper mothering instincts.