Well at 17 weeks if it were a roo I'd expect to see a lot larger, redder comb developement.  Also, in birds with this type of comb a roo will generally show three rows rather then just one down the center.  As far as the difference between her and the other bird, could be she's matured a bit faster and is not far from laying.  I also see no sign of the beginnings of saddle feathers, her feather's are very rounded back there.