Until I realize that my opposite's health is literally not changing, and that I'm doing 0 damage. This seems to have happened right after her cauterize procced -- its not counting down or dealing her any damage, it's sitting at cauterize (9).
All my damage output is being automatically negated to 0 with no listed reason (see screenshot below) and my opposite is quite able to attack me. I couldn't see any way to "win" this fight, so I recall'd out and fortunately that worked.
However, returning to the fight and taking one turn caused infinite lua errors -- I sent a bunch of them in as reports, something about attemping to index force_target as a nil value in vile life (the shade was trying to use Healing Inversion on me I guess). I tried several iterations of placement and timing but couldn't find a way around this lua bug.
Hypothesis about the invulnerability: Second Life and Cauterize procced simultaneously, and one of their "prevent all damage" flags never cleared.
Hypothesis about the lua errors: Shade was attempting to target where I used to be but not where I was now.
edit: Here's the save, too
https://www.dropbox.com/s/c1jr36vjc5mfj0e/maeryn.zip