Too bad I can't use it yet, although the 10 Swordgrass needed for the weapon was mostly a nice side-benefit of farming those Ghru for souls anyway.
With those 100k souls I got my base health up to 30, so no more one-hit kills crits by Friede. I also have 10 embers and burned a couple of extra Undead Bone Shards for good measure... if I can't beat the good Sister now, I never will.
Edit: immediately killed her. That felt almost anticlimactic.