They are all varieties of syrian hamster (teddy bears, black bears, ect.) As with all rodents, color and fur lengh are dictated by different genes. Besides the known genes that are mixed when breeding hamsters, there are modifying genes that slightly alter the appearance. That's why breeders always try to look for the purest, most perfect color, hair lengh, ect. So... that means that your sister's hamster is a "teddy bear", just not a good example of one.
When you said "mix breed hamster" I thought you were talking about the winter white/campbell hamster mix... lol