At 8-12 weeks that's a pullet. No wattle growth, pale smallish comb.
Also, it's not a black copper maran. Not sure what she is exactly, but consider cuckoo maran or black sex-link? Backyard mix? She has faint white lacing, which just doesn't happen for BCM. Any leakage for BCM would be copper colored, and they don't have lacing. Sometimes BCM hens have copper on their necks as adults. Could be a badly bred cuckoo maran female.
Marans tend to have larger combs than some other breeds, and females can pink up early with visible wattles. So it can be hard to tell on them, but in this case, I can't even see the wattles. In another month you should see comb growth and significant redness, if not, pullet for sure.