If there is light feathering on the sides of her feet then she definitely is a Black Copper Marans pullet or part BCM.
If my guess is right you'll be getting beautiful dark brown eggs!!!
I have found out that she is a BCM cross Light Sussex which the breeders have told me makes her a Silver Sussex. Are they getting confused with the original development of the Silver Sussex breed do you think?
Makes no difference to me, she is a girl and she is going to lay eggs