@nerufu: Since she did kill someone then likely yes, even in self-defense.
That said, did the dead demon never met Lily, even though from what he said he's seen Lily around before?
At least this chapter implied Evan killed that other demon then found Lily soon after on the same day.
I think she probably did not kill that human out of malice, but he still had to do his job since it was murder regardless. More backstory probably coming soon
Oof! Evan has some really heavy baggage to carry around for the rest of his life, poor bloke. And now he has two loli demons hanging around and another exorcist is complicit in covering up their existence. I hope Author-san isn't planning on making a detour off the Fluffiness Highway because there's plenty of material for a journey through darkness available.