Copper is steel blue with 2 metallic alleles. So you would need a copper, metallic steel or metallic royal blue to get copper in the next generation. F1 will give all heterozygous metallic offspring, so choose 2 steel or royal blue babies and you should get some copper back. Easiest way to get copper back would be if you bred a steel daughter back to father you would should get copper back (50% copper, 50% met steel)
Hope that made sense lol
Is the "silvery" girl copper as well? Any pics of her? If she is copper I would use her, then youll get 100% copper