@WhiskeyWolf
Most modern things rely on heavily interconnected supply chains and infrastructure, so even if she wanted to do that she wouldn't be able to so easily (in fact, if you see all the isekais where the MC brings modern stuff into a fantasy world, they always need a op skill that allows them to do things to bypass the supply chain problem). It's easier to imagine the scale of the problem by taking a look at Dr.Stone's science roadmaps. Even if a medieval society is more advanced than that, it still requires massive knowledge and a position of power/money to get the rest in place.
Not only that, they are incredibly heavily in debt. That means she can't get a loan to kick-start a business. (And when they weren't in de, she was too young to actually do anything)