I haven't been able to with any of mine but by the 1st week you will see that little comb forming. For some reason all of mine develop their combs very early. Don't know if that is the breed or just the ones that I am hatching out.
With barred and cuckoo breeds, you can usually tell gender from day one, as long as their breeding is pretty clean. If she can post a picture of the coloring on the chick's back, I can give a pretty accurate guess.