she was most likely not a order member, then we would known.
Fudge says in chapter 1. that the department thinks voldemort killed her person, since she was a very gifted witch, and she put up a real fight.
you say a lot of people are murdered....yeah, but we only get two names (+ DD), and of those two, bones and vance, bones is clearly the most important. could she RAB, or does anything else proove against that?
perhaps I'm all wrong, but i find it pretty weird, if she was murdered by voldemort himself, mentioned a lot of times, DD said she was a brilliant witch if she is of no importance to book 7. Think of it, there are other people than the head of magical law enforcement LV would want dead, so i would say there is something about amelia bones we don't know.