Black Sumatra sexing, so confused ... Can an expert help?

[MuthaCluckas]

That looks very much like a pullet to me - the neck and saddle feathers are very clearly rounded. Also still has a white-feathered face, and slender-looking legs at 12 weeks.
But, I could be wrong!

Sumatra are a slow-to-mature breed on average, but some individuals will mature faster or slower than others.
I have a cockerel that had an entirely black face, a clearly bigger comb and body, thicker legs, and big tail feathers at 8 weeks, who began crowing at 12 weeks. He was very obviously a boy, very early.

I ALSO have a Sumatra that ACTS like a cockerel, and is growing long saddle and neck feathers like a cockerel, but has the prolonged white face, shorter tail, small comb, small lightweight build, and slender legs at 13 weeks. Hasn't crowed. I'm still waiting on a definite sign to sex them. They COULD be a hen with a more androgynous hormone profile, so she's getting male-shaped feathering, but will eventually lay eggs. It's known to happen.

Sometimes you just gotta be patient.

Thank you for these descriptors! Very helpful, I am pretty confident she's a pullet but it's nice to have this kind of information for the future!