Original: Satis and the god Khnum, the guardian of the source of the river, became thought of as the complimentary deities of the source of the Nile in the Elephantine region, so Anuket, as the river herself, became viewed as their daughter in a triad for that region.
Simplified: Since the god Khnum and goddess Satis were thought to be the gods of the source of the Nile, Anuket was believed to be their daughter.