Aren't the other students plus teacher also looking for the still missing reincarnators? The pet dragon has already showed them the result might be something else than a human as well. So, it's indeed excellent luck for Kumo that the pet dragon is there. But then again, Kumo herself would have no idea the others did reincarnate. I guess it would be 50-50 for her, to either think about it or not. One thing is sure, however: She might not want to live the rest of her life eating poisonous frogs like a real spider.