I've never seen it happen, if it happened, it would show when it kills an evil?
In the top left shows how many evils have been slain and how many are in match.
If the slain evil number rises when a unrevealed card dies by Lilis, than safe to assume that Lilis has just murdered a evil.
But do remember that Lilis prioritizes in murdering good characters, so the likely chance of seeing it is if there is 1 card left.