If I pretend that her mother was a Barred Rock and that is how she got yellow skin on her body and bottoms of feet, and mistaken for one, what breed or mixed rooster could have made her have a cushion comb and black on the top of her feet and top of comb and kept the color of her feathers black?
To revisit this, if the chick came from a store:
chicks that will be solid black, and chicks that have white barring (like Barred Rocks) do look quite similar when they are young.
BUT, there is a light dot on top of the head for the ones that will be barred, and not for the ones that will be solid black. And as soon as they start growing wing feathers, the white barring should be present in barred chicks but not in solid black chicks. (Some solid black chicks will have a few white wing feathers when they are young, but it looks different than barring.)
Mixing up black chicks with barred chicks is easy if you do not know what to look for (dot on the head), so I could easily see someone at the store grabbing chicks that "look like" Barred Rock chicks. Once you know to look for the head, you can sort them out quite easily.
Comb type can be hard to see on tiny just-hatched chicks, but if you know to look for it, you often can tell what kind of comb the chick has. So that is another way this chick could have been recognized as not a Barred Rock, if someone had known to look for that detail when selling the chick.
She laid her first egg today!
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Can you post an updated picture of her? Appearance can change around the time a pullet starts to lay eggs, so maybe that would give more clues about what she actually is.