Should have died in the 100th episode. If the producers really wanted to make the series there own, thats what should have happened.
She should have died TWICE in the episode. The first half hour plays out just like it did, but when Clark goes back in time she still dies of natural causes, proving to Clark that not even he can alter destiny, and she also would have died upset with him and never knowing his secret, which would brun away at Clark's soul.