Updated photos and questions: She is 9 weeks old...and everyone agrees that she is a she...BUT she goes toe to toe with the roos in the morning. She fluffs her muff out like that one dinasaur in Jurasic park (the one that spits acid). Maybe a sibling thing but I now she's a bit older, should I be concerned?
At 9 weeks old the puffing up behavior is pecking order related. Pullets might go as far as a sharp peck to emphasize their point, but rarely take it further. Cockerels, on the other hand, will escalate to stare downs and sparing.
Your chick's comb is still very small and pale. I think it's a pullet.