It should come as no surprise that Hayley Atwell is reprising her role as Peggy Carter in Captain America: The Winter Soldier. It's been talked about and discussed a lot over the past few months.
Chris Evans was recently on the set of the film in Cleveland where he was filming a scene with Atwell as an old Peggy Carter. This confirms that she will not only have flashback scenes, but modern day scenes as well.
Atwell also recently said that she's be appearing in one of Marvel's One Shot short films that will debut at San Diego Comic-Con this year.
Captain America 2 picks up where Marvel's The Avengers left off, as Steve Rogers struggles to embrace his role in the modern world. It also stars Sebastian Stan, Frank Grillo, Samuel L. Jackson, Cobie Smulders, Scarlett Johansson, Toby Jones, Emily VanCamp, Hayley Atwell, Maximiliano Hernández, Robert Redford, and Georges St-Pierre.