Please help hen or cock?

[kettziee]

I was told she is a hen but she has started to be very aggressive towards me. She stands tall then pecks me very hard. I have my doubts of we being a hen. She is 4 months old. She is fine with my partner and does not attempt to peck him but I can't go near her anymore. This only happened about 3 days ago. She was fine before. Please help

 

[Quickster]

I'm not an expert but she looks like my ISA brown hen. and I would think that a rooster that developed would be crowing by now. I've heard people say they go through a teenage phase where they can be difficult. Someone suggested pinning the chicken down when she gets aggressive so that she knows you are dominant? I have a mean hen and don't really want to get close enough to pin her down so I haven't tried that. haha! If I ignore her she usually isn't so mean.