EDIT: I've managed to kill her by trial and error and frustration. I chugged down 3 or 4 swallows, used all buffs I had on the steel sword that I received from that side quest, and used group attack. I ran behind the folding screen and was cornered by one of the wolves, and I kept attacking it. Luckily my attacks went through the folding screen damaging her as well. I think I drank one of those instant health potions at one point too. Hopefully this helps somebody out there!

So I'm playing on hardest, and she basically curb stomps me under a few seconds every single time I try to take her down. Like, crazy fast sword attacks, like I have never seen before from any opponent in this game. How can you beat her? Thanks!