So am I missing something or why does she assume the stone is in the "demon area"? Since she moved it ahead of time how can she be so sure that it still ended up there and how much time has even passed? I really don't see how this works at all.
My best explanation is that there's more than one stone and there's been one in the "demon area" all along, but then why didn't she sell that one, because the information was slightly inaccurate? Or because she wants one herself for some reason?
Is the MC moving for a goal or just a puppet on the authors strings to "collect" more men, I see no motivation here other than protag has to put her nose in everything because protag. She should have enough money from selling the cave info. And if she needs more money, looking for magic stones seem like a good way to get killed so there's no way shed go for that if the goal was just to live a good life.
And what's this sudden monster nonsense, did they spawn out of thin air just to make MC and demon dude get closer or what, honestly it's so typical that I'd suspect the demon dude made them appear rather than author being lazy and forcing them together by nonsense.