Freaked me out the first time I saw one of my own do it when I was a kid! I thought I had another rooster for a while, until she started laying. Chickens are full of surprises.
I'm glad you got a pullet! And yes, for some reason Sebright females seem to crow more frequently than other breeds. I'm not sure why but maybe it is a side effect of the hen feathering gene that gets expressed in the males.