The Smart twins on their birthday.
The daughter of CONTROL agents Maxwell Smart and 99, and twin sister of Zachary Smart.
She was born in Washington DC in 1969 several minutes after her brother [Episode #120: "And Baby Makes Four, conclusion"].
Like her mother and grandmother her name has never been revealed.
Growing up, the siblings were unaware that their parents were spies; the fact that they lived in the only house on the block with missiles pointing at Russia apparently not being a big enough clue [Mentioned, GS95 Episode #6: "Wurst Enemies"].
By 1989 they were both attending college [Mentioned, TV Movie: "Get Smart, Again!"] but after this nothing is known of her.