Miroku wanted Shion to live a normal life and prevented her from learning about her true powers, and as such prevented her guards from teaching Shion any ninjutsu. But to protect her daughter, she left Shion a special bell which allows Shion to foresee her own death in the future and be able to prevent it. However, to save Shion's life, another one must usually be sacrificed in her place.
Eventually, Miroku and Mōryō came into conflict, and when the demon tried to absorb Shion in place of Miroku, the mother sacrificed her own life to save her daughter and seal away Mōryō.
Miroku seems to be extremely good at fuuinjutsu. Was able to seal their energy in an amulet that would later be handed over to Shion, protecting it under any situation. More than that as a priestess, she was able to seal anything when using the Shrine Seal. It is likely that it also makes use of the Future Telling, being a blood legacy.