I don't see Harry agreeing to use Bella as a tool.
Why not? If it's not a use that harms her directly, just letting her make an appearance from time to time to scare people into voting Harry, why wouldn't Harry agree?
After all, even Quirrel's (possibly just pretending) psych healer fixes her, she's not likely to ever become part of civilized society again. She should have some purpose to her life, no? Both helping the Dark-Lord-Harry (if not healed) and helping her rescuer Harry Potter (if healed) would please Bellatrix herself too. I really see no downsides to using her in this way.
Oh, I'm sure you and I can come up with lots of rationalizations to justify using her. Problem is, Harry, in addition to being a rationalist, is also a fictional character.
Eliezer, through Harry has, thus far, had a certain sense of poetic justice. Using Bella as bait would go against that. The same drive that leads Harry to see himself as the mesiah of two worlds -- the man who will kill death, that same drive will balk at using Bella. It's too ugly.
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.