hmmm, do you have a Rooster? I've had my share of weird eggs, but don't know what a fertilized one would look like as I don't have Roosters...
No rooster, maybe one but he's too young for that. I've been researching and apparently it's called a wind egg, just cos it was her first go at it, no more have come from her since, no eggs at all, but at least she tried haha