Actually, i think the differences between Eric and Nell’s responses to post shooting trauma are important, because Nell’s response to killing a man was her inability to stop thinking of her victim as a person, and those who know him and love him, it was a reaction based on the behalf of others, but Eric’s response is more self based, he’s shaken not because of the victim, but because he killed him.
So, Nell wasn’t explicitly bothered by her ability to kill as much as she was suffering from feeling compassion to those who would be hurt by her would be killer’s death, whereas Eric was explicitly bothered by the fact that he acted and killed somebody.
It’s why i personally think that Nell is suited to field work and Eric isn’t, Nell’s never shown any real self doubt or self disdain towards her ability to kill somebody, whereas that was Eric’s reaction entirely. Eric didn’t like that he killed somebody, it was a self-centered reaction (that sounds judgmental, it’s not, i think most would react the way he does), and i feel like having a reaction of compassion towards others after killing somebody would be easier to work through than it would to work past having a genuine disdain at your own ability to kill, which Eric appears to have.
Nell is traumatised because a man is dead, Eric is traumatised because he killed a man, big difference.