Sister Svalna is the mini-boss Valkyr at the end of the gauntlet which leads to Valithria Dreamwalker.
Initially mistaking her for gauntlet trash, I found her to be an exceptionally difficult solo kill, harder than some of ICC's real bosses. She has a boss ability that kills you 40 seconds into the fight. So, that is all the time that you have, and she has 1.56 million hit points. If there is a way to mitigate this ability without despawning her (and she is quite prone to despawn), I have not figured it out.
I couldn't tell you if this is a world first. Unless I'm missing some way to mitigate her special ability at 40 seconds, she is so difficult to kill that I would have expected anyone who had done it to have put up a video or something. I can't find any.
So yeah, big fat DPS burn below. Bigger than I'd imagined possible, until last night.