I actually don't want Diana to kill anybody else for a long, long time. Not because it would be "wrong" perse, but because I loathe the "slippery slope" argument.
Basically, the (imo, extremely idiotic) idea that if you ever, ever kill anybody (even an irredeemable genocidal monster), for any reason (even self-defense, even to save the world), you are always going to become a cold, ruthless murderer who is forever unable to hold back and casually kills people even for minor crimes because you can't understand the value of life anymore.
I like how Diana is the living proof that "no, killing doesn't necessarily make you evil; no, if you kill once it doesn't necessarily mean you are going to do it again; and no, you don't have to regret your actions nor atone for them". I want her to stay that way.