I tried fighting Umbra at level 8, and she whooped my ass. I couldn't even get any power off her. After some trial and error, i figured out an AI glitch to kill her. I danced around the fire pit and backed up, she then jumped into the fire pit and i blasted her with some magic out of my staff. For some reason it paralyzed her, and she just stood in the fire while i continually fired my staff at her. She eventually died from standing in the fire, and much magic bolts.
So now i had this kick ass sword at level 8 that tore through anything i fought. The game soon got way to easy, and not as fun. I thought about just bumping up the difficulty, but then that would render my bow useless in comparison, and i really like using the bow. So i opted to reload a save before i got to her, and leave the sword and armor alone until i could legitimately beat her.