Photos of your chicken help a lot.
A Barred Rock hen can produce not-barred daughters if the father of the chicks is not-barred. So it could be an honest mistake on the part of the egg seller, if some other rooster got in with the Barred Rock Hens. (Although they really should be more careful.)
Barred Rocks usually do NOT have black face and comb, and the bottoms of their feet are usually yellow even if the legs and tops of the feet might be dark.
Small chickens with black faces: Silkies, Sumatra bantams, even standard-sized Sumatras are fairly small. Ayam Cemani are on the small side, and well known for being black all over. There are probably a few more that I'm forgetting, too.
Silkies have odd feathers, but when crossed with other chickens you get normal feathers on the chicks. Silkies have feathered feet, crest on the head, an extra toe on each foot, and often muff/beard under the chin, in addition to the black skin. Chicks that are part silkie usually have at least some of these extra features. So if she's part silkie, it will probably be pretty obvious.
Do you have any idea what other breeds the breeder has? For example, if you bought the eggs on ebay, you could look at what other breeds the seller lists.
