@Mrs. K - An update on the integration! Betty (new girl) went into the coop for her first full night on Christmas Eve; I put her on the lower floor, while the main flock slept upstairs. In the morning, the lil rooster lad had a minor scuffle with her but nothing more than a bit of intimidation and light pecking... everyone else was fine. The second night she went in on the top floor with no problems!
Since then, I am not sure if she is just becoming more confident, or if her personality is changing due to hormones, but she has put the fear of god into the original flock and is picking on them all. One is absolutely terrified of her and won't be anywhere near her full stop.
It could be just trying to establish her place in the flock, but I've got concerns her behaviour might be because she 
isn't in fact a pullet.
Betty has started pecking the others - hard - sometimes right on the spine. She has challenged the roo by running at him, as well as the others too, and steals food from them while they are eating. She has particularly scared my fave little gal Jacqui, and follows/stalks her all the time, and has grabbed her by the butt feathers a handful of times, which is what my roo does to Betty (I believe his is a mating attempt) Two of them won't even eat near her, and Jacqui keeps running to me for protection from her. This morning Jacqui wouldn't even come out of the coop and ran back inside as soon as I brought her out, only to have Betty stalk up to her her in the coop (Betty has NEVER gone in the coop on her own) Jacqui shrieked and panicked, flapping around terrified and ran out. Jacqui normally challenges the roo so it is sad to see her so afraid! I have seen no major fighting etc to cause such extreme fear and I watch them all day every day.
I know this could all be just dominance and pecking order adjustments, but I have had a niggling feeling I cannot shake that she is not a pullet - I have had this feeling since the day we got her. It was a gut feel at first, and I didnt like the look of her tail... but then a few days after we got her she had really dramatic comb and wattle development; we're talking nothing to HUGE in a matter of a week. Her crest is round, and no sign of streamers, so kinda confusing...
I posted pics on some facebook groups, and was told by a breeder
 "she is a girl full stop" (quote) and hens can have big wattles and comb due to mixing in breeding... which I know is true, but from what I understand it is rare or at least very uncommon. Anyway since the breeder is more experienced than I am it put doubt in my mind, but my concerns never left so I am sending in some DNA samples today.
I am attaching some photos that show the dramatic wattle and comb development as well as her tail. Photo one is a couple of days after we got her, then the rest are dated from there if you open the pics up. Note she has had a trim around the eyes in the last two comb pics so those pics might look a bit weird in crest shape.
I'd appreciate any insight you have into either her gender, or whether or not this behaviour is normal pecking order stuff... Thanks so much, and good luck with the article!!