I just did this trick someone put on the crap edition of Elder Scrolls wiki: Went back into the tunnel I came from, shot the forget out of it with arrows, and my Follower kept hitting it in the knees, which I didn't expect. I also used some potions for armor, true shot for more arrow damage, etc. IT actually went down relatively easy after that, 2.0x sneak damage...
Should I become a Werewolf? They're about to make me one.