Why don't they demand relief from the royal family? They arbitrarily opened trade without consultation and due warning to the Northern families, and now they have a massive monetary shortfall - it seems the eastern country they're trading with benefit more from the trade than they themselves do if massive swathes of the people are going to starve to death because of it.
So she just said she remembers the future and that the herbs' price will stay consistent. Then suddenly she's surprised that the price plummets.
I love this type of story but this one seems even less polished than usual
She states that she's at the tail end of the story, so it may be that while she 'knows the future', she knows it in far less detail than she really needs. This is just me giving it the benefit of the doubt though, as the story should have stated as such if she's going to say "she knows the future", and then immediately contradict it.