Hayley Atwell says that despite online reports to the contrary, she will be back in the role of Peggy Carter in the sequel "Captain America: The Winter Solider". However, she remains quiet about the extent or nature of that involvement:
"They're so tight, the Marvel family, and private. I can say that I am involved in some way in the second one. Just know that it's not me being cryptic, it's Marvel. They can just as easily kill me off if I threaten to tell the story before it's time. They're keeping it all under wraps."
She does, however, confirm we'll see more of Peggy in what sounds like another Marvel short film:
"Marvel have made sure that as part of Comic-Con there will be a little kind of snapshot as to what Peggy's actually really capable of, which was finished here [near Shepparton Studios] and which was great fun. Hopefully, it will lead to other things."
Source: The Age