Breed?

I got some eggs from my aunt a while back. She only has white leghorns and sapphire gems in her run, nothing else at all. The rest of the chicks I have from the clutch are typical; spotted (mixed) leghorns and gems. Yet this one perplexes me… solid black,,, I assumed she could be a Black australorp, but it makes zero sense,, how would that happen from a closed-breed flock? And that wouldnt explain the strawberry comb. Any ideas??