Immortality doesn't mean you can't die or not wish that you'd be rather dead. There's always loopholes and many ways to deal with it, which is what Kumoko referring to in this very chapter (and goes at length about it in novel), even if you disregard some skills within the system itself, not to mention some other irregularities. Like she said so many chapters ago, there's always someone stronger.With that said, what's there at stakes here? Every fight become meaningless because she can just win every fight by redoing it enough times
Well, it's just the way the manga is drawn. In the LN illustrations (and in the anime PV) you can see that she does have cephalothorax and abdomen only, no separate head.Also, I'm not a specialist in arachnidae but the fact that she has an abdomen, a cephalothorax, and a head , means that she's not really a spider, right ?