She lived far longer as a normal, quiet high school girl. As a spider monster, she behaved more like a gamer, but that was under those different circumstances, being separate from a civilisation. Even when she started to hang around the city, she was still nothing but a monster, and she knew it, with no means of communication with the humans. How long was she a spider before reaching the arachne point? Not even a year. If the reincarnators had suddenly been returned to Japan back into their 100% normal human bodies, I doubt Wakaba would have continued to act so wildly and willfully either. In other words, she didn't really change, she just returned closer to what she used to be before the be-a-monster vacation.