i don't think you're supposed to kill it, but i just normally hit it with a firebound ebony battleaxe, which can be found somewhere in the level. it's not supposed to die if you want the reward. if you want the reward, you only need to break the ward, which has 15 health, and then use the first two words of the Kyne's Peace shout, which are all in the level. the shout's words are kaan drem ov

I normally type

Mulaag

Mulaag

to break wards, then 

YOL

Nos

Nos

Mulaag

something of the sort