Cosplayer Jaime StoneDead recently posted a photo of her amazing Big Sister outfit, taken by photographer Postmorbid, to the Bioshock subreddit. Giving some more detail in the comments, Jaime says she "worked on this off and on after my day job for about 3 months and all day on the weekends." It's a pretty complex outfit, with a helmet that lights up as well as being "rigged with sound so I could screech at people."
Unlike the Big Sisters in Bioshock 2 she probably can't go for a swim in that getup, as she only has "about 70% vision" in it and says, "My main struggle was hearing and ample ventilation."
You can see more of it and Jaime's other cosplay at her Instagram page.