I did too had many problems with this monster.
I had a 13 Speed and 10 Brawl. I also had the Spark of Life and Sear for extra damage and also a Reposte.
There was no way to defeat this foe. I had to wait and play again and again until i got enough damage on the first few round.
I couldn't change any of my gear since it was already the best and i mean the best i could find and there was no way to acquire some kind of potion to raise my strength.
So i did the same combat over and over again until i got lucky. Not a very pleasant moment in the game.