Congrat's on your beautiful black cochin.They are awesome bird's.The hen's are very good broodie's and I never had any problem's with my roo's cept one but He was our Fav. anyway.Hope he does good for Ya.
This bird will not change her breed if many people say Cochin or Brahma.Her head looks Pea combed and legs are havy feathered like Cochin.Now we do not need to guess more,we need comb picture if OP want to know the breed.
These are not good shots at all but I am 99 percent sure she has a single comb. It is a single bumpy strop going up and she has very little comb to speak of.