I had 2 Bluebell hens along with a few Leghorns, a RIR hen and some bantams. The Blues were not top of the pecking order, but they were not bottom either. They got along well with everyone else, showed no aggression and I found one to be very, very friendly while the other one was more skittish. Like us humans they have their different personalities.
I think in your situation the hen was simply sorting out her position in the pecking order. She was there first and she wants to be on top. You did not say how old the new chicken is, but if she's more or less the same size as the Blue she should be fine. With most chickens, regardless of breed there will be some squabbling when you introduce new members to an existing flock. Ideally you should keep them separate, but within sight of each other, for a few days at least before letting them free range together or like the above poster suggested, coop them up together at night. I have not tried the coop up method myself, but I found free ranging them together works well.
I would also suggest, if you haven't already, that you deworm the Blue (and the newbie since they've been in contact) and dust for mites as a precaution, since you don't know where she's been and what she may be carrying. Chickens can carry all sorts of nasties without showing any sign of it. I learned that lesson the hard way!