Culmanic Parts - Worlds of the Timestream: The Throne, #1

Two long-lived and hard-to-kill men, Samadeya-Qayin and Pelik-Qayin--the alternate continuations of the repentant and unrepentant Cain respectively--have always been deadly enemies. For the last millennium they have duelled over the High Kingship of Ireland. Here are three of their stories:The Prologue: In the early eleventh century, Brian Boru is rescued by Cormac Meathe and Catherine Neal at Clontarf.
Cormac and Catherine are subsequently elevated to the throne. All the King's Horses: Kate the Culmanic, a fourteenth-century horse girl descendent of Catherine, becomes High Queen. Mother's Girl: Mystery woman, prodigy, and national heroine Amy Rea is the adopted daughter of super-spy Carlan Rea. She renames the Culmanic "Science" and makes it her own. With nine unlikely friends, Amy takes the Royal Academy at Tara by storm, suffers profound betrayals, then joins the Royal Army Naval Corps.
Who is she, why is she The Mother's Girl, and why have the Assassin's Guild accepted three contracts on her life?