Eleanor Lamb

From BioShock Wiki

Eleanor Lamb was the first Little Sister successfully bonded to a Big Daddy, the Big Daddy in question being Subject Delta. After 10 years, Eleanor grew up without her Big Daddy and will be one of the few mysteries of what happened to them in Bioshock 2 (it is possible that Jack saved her in the original BioShock). We know that Sofia Lamb's Rapture Family cult worships her, in Siren Alley what is presumably her dress can be seen preserved under a glass case. Eleanor is of great interest to Sofia Lamb, and she and her recruits are actively searching for her. It is speculated that Eleanor is Sophia Lambs daughter (they share the same surname) and that she is also the original Big Sister. She seems to have a similar dress to the young woman in the Teaser Trailer, suggesting that she is Eleanor.

Eleanor still remembers Delta after ten years and knows he is searching for her. Throughout the course of the game, she will leave him gifts and messages written nearby.