Rosebud

From BioShock Wiki

The Splicer model "Rosebud" is a female factory worker frantically looking for her lost child, who might have been taken to be made into a Little Sister. She cries out to her child, or for her child not to be taken from her, when she is not singing a broken version of Amazing Grace. She also frequently refers to the player character as "monster".

Rosebud is the most mutated Splicer model, with one side of her face horribly consumed by a roseate tumor, from which she likely gets her name.

Rosebud is the first splicer to appear in-game, slaying Johnny as you first arrive in the city; but she cannot be fought until you reach Neptune's Bounty, where she lurks around the entrance to Fontaine Fisheries.