I read Harry's suggestion not to investigate, and her responding smirk, as indicating that's it's already tacitly understood that the good guys actually killed the death eaters somehow.
Yes, but she's likely to be interested in how it happened. Allowing the 11 year old Harry to keep it a secret towards her means to give up power to Harry.
Keep in mind that Amelia herself is a powerful witch, and thus "you are not meant to know" is kinda-sorta expected in those circles, and a most valid excuse for basically anything weird or unexplainable.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 119.
Plans for next chapter release:
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)