I'll add I forgot I've seen someone put food coloring on their bum and if the egg comes out with that color streak on it you'll know too. May be worth doing.
That was going to be my next question, a full body picture as I know they differ in coloring according to the SOP. The only way really to tell is to isolate and visibly see that it's laying. Is it crowing at all or any other signs of not being a hen? I asked my mom a minute ago if she ever had...
Anyway you could isolate this chicken and see if it's laying? I had one about 8 years ago that was 100% a hen but had a rooster like comb and looked very masculine but laid eggs(Buff Orpington). But, this one honestly looks like a rooster. This is interesting👀 I'd like to see what opinions...