So I will be the devil advocate... no, i won't defend the cat girl, this is about my opinion of the arc.
I am enjoying the idea of this arc, this mangaka has amazing skill in drawing fantasy genre and this arc gives him the chance to flex his skill a bit as the original world of Tsugumomo is grounded on reality, but i admit there are many things that aren't being well done in this arc, i would write some of them but you guys know well what they are the pace being i think being the one that is really affecting us all, even so i still have hope for what it will become in further ahead for this arc principally when they kill the scum slaver.
I was thinking of doing a joke to end this comment but sincerely i suck doing jokes so I will spare you of my terrible jokes and be direct, calm down a little guys, i know this isn't the best arc until now but don't let yourselves be dragged in the hate, it isn't healthy. As too much of the internet is already overtaken by hate, don't let this site be too.
And yes... I too think cat girl deserves death, i was being naive in giving her a little comprehension on my head but it is clear that even with her reasons she doesn't deserve a second chance, I just hope the little sister stay safe ( which is a little redundant as all this world is just an amasogi )