The recently updated Captain America: Winter Soldier page on IMDB.com is now listing Samantha MacIvor as the personal stunt double for actress Branka Katic in the movie. However Branka Katic is not mentioned in the full cast list for the film; in both named and unamed parts.
So who is she? She must play some importance in the film if she has her own stunt double just as Chris Evans, Scarlett Johansson and the other principal actors do.