Margrave
This isn't just killing a character, this is a shock death for both the character and the reader. (Arguable fridging since you are likely going to use her death to hurt the mc.) The mc may have been in a precarious situation so far, but none of the female leads have been in situations that maimed or nearly killed them so far and the reader knows the mc can't die because it'd end that novel, so there's no real expectation that important characters can die before you killed Emilia off, which is especially bad since she's gotten the most screen time of any female lead so far. (Some of this is bringing up my earlier topic, but it feels especially true now that I've read this far.)