Assuming Oka is the elf reincarnated teacher, I'm also of the opinion that she is generally a decent person trying to help her students. I think that's kind of admirable that she is doing so fifteen years after they existed in a 'normal' student-teacher relationship. It can be called playing god by deciding who lives or not, but it seems like old fashioned vigilantism to me.

What was the strategic importance of the Elf village, again? Are they in the way of the demon lord's army?

To pile on just a bit, the animation was embarrassing this episode.