I don't think you can tell from the photo.
Take a reallly close look at her comb, if it's flat with a point on the end she's a Dom, if it's bumpy all the way up- like the teeth on a comb, she a Rock.
Edited to add for blue fire: Both male and female barred chicks have a white spot on the back of their heads, male chicks tend to have a larger more irregular white spot that may even end in a collar around the neck. Females tend to have a smaller more distinct spot and are usually darker in color. But this is not a 100% accurate way of sexing barred chicks, there are many exceptions.