So Kumoko would take over the demon lord or assume her shape because Ariel's an already established ruler of the monsters? Easier to use her existing position/fame than to replace her as a totally new monster. I can't say I'd feel terrible sorry for her. But if that's the case, what is the pale lady? A random vestige that happened to develop much better than the rest? Or maybe something Kumoko was using during the process of taking over the demon lord. If the 15 years later demon lord indeed is Kumoko, then it doesn't really need to be pondered how the demon lord would have something related to Kumoko serving her. It would just be Kumoko serving Kumoko.