Sorry in advance for any typos! Using my phone for responses makes participation difficult, lol. I was wondering if it may be Embracing Ice by Yabou.
It is rated MA on this site, so no YIMS.
It's somewhat a match to what you describe, especially since none of the other suggestions have fit so far.
Embracing Ice by Yabou
[COMPLETE] She had never known his past and had never really wanted to, but its hard to hate someone when you see the truth. If only the well had allowed her to live in the lies she had built up around him, her enemy...Her Sesshoumaru...