Do you have pictures of the chicks as adults? Recessive white is always completely white; so if any of the white chicks have black spots or red leakage, then they’re definitely from the leghorn.
The chick in the first article looks like a regular, two-winged chicken. :hmm
You say “like 6 months ago” as if you’re uncertain. Are you absolutely sure that you’ve had her that long? I know it’s improbable, but my guess would be that the father of her chicks is one of the roosters from that farm.
She’s a beautiful hen! Do you have more pictures of her?