She's "such a different character" from Booker and so it would have been a "most awful betrayal" to make her just like him, as she is a "much more thoughtful person" and doesn't just charge ahead.
Elizabeth won't suddenly grow bulging biceps while she runs around with huge guns - no double pun intended.
"With the player getting the opportunity to see how Liz is experiencing the world through first person, we have to be ever so careful to not betray what the player has already experienced of Liz in Infinite and what they’re going to experience of Liz in the first part of the DLC,” explained level designer Amanda Jeffrey to IGN.
“That’s always foremost in our mind, because Liz is such a different character to Booker, and if we were to just put Booker in a dress, then that would be the most awful betrayal of what we’re doing for Liz, and players would just feel like it was a cheap way out, and that’s not something that we want to do. So we don’t have all of the answers yet for it, but we are very, very, very much aware of all of the dangers that we need to try and avoid.”
“Booker, as a character, is an ex-soldier. He’s very much about storming the gates, or taking it head on, and he has these other tools available to him, but generally he’s all about going head to head with his enemy and taking him down because he’s the stronger man,” she continued.
“Now, even in Infinite, Elizabeth was a much more thoughtful person. She would be more considerate about keeping out of danger, and assisting you with various different things, and looking for things around in the environment and keeping an eye out for stuff. She’s more aware of her surroundings, and how she interacts with those things."
"She’s the one who’s rifling through the drawers, or leaning against the walls, or whatever it is that she may be doing. And for that to transfer over to gameplay is, I think, we would be betraying her character again if suddenly she’s got these huge biceps and she’s running around the place with a ginormous machine gun.”
Ken Levine added that Buried at Sea was "more toward a survival horror game" than first-person shooter. Burial at Sea explores Rapture on the eve of its fall, which takes places considerably before the original BioShock. It makes up for two of three planned DLC packs for BioShock Infinite and is split across two episodes.