I will never, ever agree that an inability to kill makes a character terrible. Killing, for most people, is a very difficult thing to do. Turning someone into a killer, if they aren't a psychopath to begin with, requires breaking down a lot of the natural inhibitions against it that any decent human being would possess. Kendra was a barista six months ago. Even in her past lives, apparently, she relied mostly on Carter to defend her, in keeping with the cultural values of the times. She's had some combat training and experience, she's participated in battles where people died, but deliberately killing someone with premeditation is not something that should realistically be portrayed as easy for her, no matter what's objectively at stake. Not to mention that, if I understand correctly, she would've been condemning Carter not only to losing his memories, but to never again being reincarnated. After 4000 years as his soulmate, how could she be expected to just coldly set that aside? How could she even be human if that were easy for her?
If every character in every show were just some cold-blooded psychopath who could murder without a qualm and dismiss love as an inconvenience, that would be horrible. If every story portrayed brute violence as the solution to every problem, that would be atrocious. It is never a terrible thing to be motivated by love or compassion or respect for life. There can be situations where it's regrettably necessary to set them aside, but being unable to set aside mercy and humanity is something that should never be denounced. That doesn't make someone terrible, it makes them too good for the situation.
According to Wikipedia, the recent comics have given Savage another daughter, an FBI profiler named Kass Sage, though sources disagree on whether that's short for Kassandra or Kassidy.