She holds a monopoly on the new scalpels, customers will wait because they don't have any alternatives. They still have their old scalpels as well because you wouldn't get rid of your existing stock before your new ones arrive, otherwise you couldn't do surgeries.
In the worst case scenario, literally nothing changes for the doctors as they'll continue using their old scalpels.
Iron being a commodity, you can just go buy it from other customers as well, just head to any blacksmith with a low customer count and buy their iron stock.
Given how small scalpel blades are and how little iron they use compared to the manpower needed to make them, you'd be completely stocked for a long time with very few ingots.
This delay is a non-issue, the biggest impact is on the blacksmith labor force who can't work waiting for raw materials.