Sheryl is the force-growth clone of Ranshe Meis, built by Grace, whom's been working on this con since way-back-when. Ranshe is, in turn, the mother of Ranka and what's-his-face, the cyborg jet jockey (who also doesn't remember damn thing, now that I think on it).
Sheryl was planted on the streets of Galaxy by Grace or her accompliceses, while Sheryl still wasn't quite sapent, and left to form memories of suffering, as part of the conditioning to be Graces tool.
Grace when through 8 test tubes getting this project off the ground.
Sheryl's last name was chosen 'cause Grace, like all Brainy Villains, is big on Irony . . .
(Ozma could have been Ranshe's in-law. Or not . . . )