What does the bag actually contain? The plates to manufacture notes? I might not be remembering correctly the scenes in the past, but perhaps the girl doesn't actually have anything with her that would be instantly worth robbing, not enough hard cash anyway. It could be that even if they robbed the plates, they would still actually need the expertice as well to be able to use them for anything. And that's why they would rather get money, one way or another, than just rob the girl.