Gorgeous bird.
At 19 weeks, I'm guessing pullet.
Her mom may or may not be a Barred Rock, I'm not sure. But her dad isn't a Barred Rock.
Explanation below.
(Picture examples)
My Barred Plymouth Rock pullet. Black bird with white stripes ("barred" = white stripe. Any breed and color can be barred)
Second picture = 2 solid black pullets. One is the daughter of a barred mom.
Barring is sex linked.
Barred mom x non-barred dad = daughters not barred, sons single barred.
Barred Hens can only pass barring onto sons, not her daughters.
Barred Roosters can pass barring onto anybody.
Black is a dominant color. If one of the parents is black feathered, there's a possibility the chicks will be as well even if the other parent isn't black.
(*keep in mind that Blue, Chocolate, and Lavender, are all black based. And white can hide patterns and colors.)