Was Carol Marcus' appearance purposefully made to be identical to Elizabeth Dehner, so that the fans might guess that the bad guy was going to be Gary Mitchell?
I think the choice of haircut may have been deliberate. The first two-part IDW "Ongoing" comic, which featured Gary Mitchell, promised "easter eggs and red herrings" and there was a even reference to Dehner and McCoy having been lovers
in the past of this timeline. So I was actually expecting we'd see Dehner in the movie, to give a little tension to McCoy's scenes. Suddenly, up popped Alice Eve in the Dehner hairstyle for the movie's pre-publicity!
It may have been as innocent as the movie's hairstylist going back through old episodes for inspiration on Carol's "look". They did a variation on the large, pointy bun in the last film (on an extra in a red dress that people wondered was supposed to be Janice Rand - and then the comics reused that style when they put Rand into their cast of new characters).