Apparently from the late 90s to the early 00s, Lex Luthor had a daughter. I was completely oblivious to this fact until I read Superman Villains Secret Files and Origins. I looked on the internet and apparently this daughter was aged up into a teenage iteration of Brainiac in Our Worlds at War, was featured in Chuck Austen's Superman Metropolis, and apparently was never seen again.

Why did this character stop appearing in the comics and how would you incorperate her into the current Superman titles?