She is not a Black Sex-link, as those birds are black with gold on their neck. In fact, she doesn't really look like any breed that I know of--she's probably some sort of mix, or a Canadian breed that I, as a United States resident, don't know much about. She's a pretty bird!
Kind of, but not really. The birds in my avatar are Light-Brown Dutch Bantams, which, as their name suggests, are a bantam breed originating in the Netherlands. They are relatively rare in countries other than Europe, though there are a few breeders in the United States. Your hen does not share some of the distinguishing characteristics of a Dutch Bantam: slate legs, white earlobes, a partridge/black breasted red color pattern, and reddish bay eyes.
It is odd that a supplier would have been selling mixed breed chickens. It could be that your hen is a Canadian breed that, as a person in the United States, I and others don't know much about.