I took that more as her being super rich so she can't relate to the poors who can't easily farm up a couple million yen in an afternoon.Like when they were talking about how expensive it is and she's just "Just go farm dungeons for a bit if you need the money" shows she doesn't really grasp the importance of preparation; what happens if you can't go farming because of the status effect lady.
I went back to refresh on how she's portrayed. I wouldn't call her a meathead but she is pretty consistently shown to be arrogant about her abilities so maybe she was just being arrogant here. I still don't think it's good story progression because it makes her look really stupid and unreliable. Honestly the best twist would be that she actually bought up all the dispel items ahead of time and this going to shops to find its sold out was just a ruse to force her lackluster but talented party to push ahead in the dungeon.