It might be:
Beneath the Light of the Moon Reviews
Kagome returns to the Feudal Era and finds that the past has fallen victim to the Dark. An ancient evil has escaped its prison and it seeks to extinguish the Light and Kagome finds herself a target. The Western lord stands at her side, unwilling to allow the Darkness to possess the beautiful priestess or destroy the future he intends for them. TEMPORARY HIATUS
Rating: MA
Kagome uses I think a flower called the Midnight Orchid (The flower is actually called the dark moon orchid) to save Rin. This was written by Inari.
EDIT BY WICCAN: And here is the link: http://www.dokuga.com/fanfiction/story/6070/1