Not much is really known yet about Agent 13, aka Sharon Carter, but she made a lasting impression in The Winter Soldier. Enough, it seems, to have been bumped up the roster here, forming a part of Captain America's team. Anyone with the surname Carter is immediately going to pique interest in this universe, and though not confirmed it's expected she'll be related in some capacity (it's great-niece in the comics) to Peggy. If that is the case, then her relationship with Steve Rogers is going to be pretty interesting to watch, and she's a character who could develop given more time and films. Looking at the line-ups, however, she seems a little out of her depth. The closest comparison is Black Widow, but she's been working with the Avengers for years now. Carter doesn't have that sort of experience, nor any powers, and that alone puts her at risk. It may be that we see two Carters pass away in this film (and if we do see Peggy go, that's going to be all kinds of emotional).