I actually didn't like that Molly killed her. Thought it was quite random to be honest. Neville would have been good definately but like you said amm, it's not really his nature. I am vexed that Lupin died without so much as a decent last scene so I think he should have died a hero by killing one of the most hated characters. Plus he had skillz enough to kill her.
I loved the taboo too. The part was genius. I think the book turned around when Ron reappeared. Lifted the mood.