most likely a girl by the looks. If you don't plan to butcher Bertha or sell/give her to someone who will, you will need to separate her from the brooder ASAP, and put on grass (if you aren't buried in snow) and feed rationed feed in small amounts until spring comes and you can put her on grass and free range. Cornish are notorious for over eating and growing too rapidly and their legs giving out on them or even breaking or dislocating the leg/hip joints. Just wanted to give you fair warning if you plan to make a pet of Bertha
I just googled how to sex cornish rocks and looked at pictures, I seen pictures of 8 week old hens and their combs are bumped up and red, just like a 5-6 month old 'regular' dual purpose hen would be. Then a 4-5 week old cockerel who had quite a big red comb, SO I am pretty darn sure its a girl if it is 6 weeks old and I see no facial growth or coloring at all.
I agree with needing to separate her because this girl can eat!...She will eat laying down and that is something to see. But we have frozen ground, Not complete snow, it is supposed to get up to 35-40 this weekend so I was thinking of putting her with the big chickens however she isn't fully feathered and she may get too cold. How soon do you butcher a Cornish Rock? And do you notice she is sitting on Clementine?