I don't think it's strange of her to require sanitation standards when she does have the knowledge, regardless of this world not knowing these things.
Also I'm not entirely sure that this world doesn't have a standard for sanitation as I've seen some comments say. Although this world seems similar to ours, we've seen before that not everything has a one-to-one correspondence. So if they'd already discovered that washing hands after going to the bathroom and before handling food prevents disease, I wouldn't be surprised.
Also she also has other partners she doesn't have problems with. I'd like to imagine she was thorough in her decisions to partner with them, so she would've inspected the businesses the same way. Which means they passed her standards, so other businesses do have good sanitation practices.
But also I wish the author would introduce subplots a little more smoothly lol.