Originally posted by GoldieHeart:

I don't believe that the Frost Caves respawn the fenris hair. Be sure to use your bow to get down any fenris hair that is hanging from the ceiling as well as the hair that is actually hanging down and can be gotten by pressing E. Sometimes you can also get the hair by slashing it when it's not that high upon the ceiling and can't be gotten by pressing E.

Ah, heck. That's gonna make it more tedious, but thanks for the answer!