Well, I don't think Ember would think Shuna made Lehrigen a moot point. After all, Ember's tribe is an ocean away, and who knows when they'll see Cutter's half the tribe again?
I can see Ember's visionary abilities making her "obsess" with Lehrigen a bit. After all, he's their best hope for really making a place for themselves in an increasingly human world. Funny, then, that the author lets the whole thing sort of peter out by not having Lehrigen come back to them till he's dying.
As the murderer of Kahvi, I agree, it's too convenient. I somehow can't believe that Kahvi died that way, if she died at all. After all, shouldn't she have died about 7000 years before? (If she really has wolf blood, that is? )