Really hope they aren't just deathflagging her like this. I said from the very beginning this is probably the highest the stakes have been for so many human/elf characters that at least one waifu is probably gonna bite it this arc.
Pretty sure she meant that nobody is old enough to remember what Flamme was like as a smiling young girl, not even Frieren, because that was before they met.
Can't speak to how it might work in your country, but my understanding of the US military is that you are "expected" to follow the Rules of Engagement and any international laws on war crimes that the US officially recognizes, regardless of whatever your orders are. So while yes, you are allowed to act independently if chain of command breaks down or communication is impossible, that doesn't mean you can do whatever you want with impunity. Obviously people will fuck up here, intentionally or otherwise, but that's why court martials exist.
The way the Shadow Warriors seem to operate is that there aren't any rules of engagement and they don't answer to any laws. They could basically kill anyone at any time for any reason they deemed fit without having to answer to any political authority, not even the emperor. That's less like a military body and more like a secret police.