Originally Posted by Larry Borgia
Didn't she start as a real person, who got more and more artificial through time?
Indeed—she apparently received her first "prosthetic body" as a child, retaining only her natural brain. (Or part of it, at least. From what I remember, by the time of the movie and whatnot, she doesn't even have all of her original brain. I don't know if that happened after the original cyborging, or at the same time.)
The second season of SAC is supposed to have an episode where we find out why she ended up becoming a cyborg in the first place. But that's all I know.