I'm not entirely sure that the huge youki was that of the newly awakened being.
It could be that Clare got the memories and the thing awakened, or that Clare got the memories and it's her youki that became this massive.
I like the second possibility more. Because otherwise it's just another super strong awakened being. Now that Isely is gone we can probably use one and this awakened being is interesting, but you can just let strong monsters pop up pretty easily. Bringing Clare up to this level is harder to do, so I hope that's what happened.
Plus, she could get a powerup and the thing could simply awaken the next chapter.
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"