Who is Siona Ibn Fuad al-Seyefa Atreides from God Emperor of Dune and what is their importance?

Siona Ibn Fuad al-Seyefa Atreides is the only one of nine rebels to survive raiding the God Emperor Leto II's Citadel and stealing its plans and some personal journals, Siona is beautiful, athletic, and shapely, having the classic features of an Atreides: a gently oval face, generous mouth, alert eyes, small nose. At a young age she is sent to attend the Fish Speakers' School at Onn, where her teenaged rebelliousness worries her father, Moneo Atreides, Leto's majordomo and closest aide. Even as a student, Siona rejects Leto's divinity and the idea that the Worm takes over in times of violence and alone is morally responsible. Leto has bred Siona for a special place in his Golden Path, and allows her to rebel until the time comes to test her and see if she will accept her fate.