I think it's also important to emphasize for kids that polite is not the most important thing to be. If it would cause her pain or distress to eat something, she's not obligated to eat it; politeness has given way to safety and health, which are higher concerns. And if someone wants you to sacrifice *your* safety and health for the sake of *their* family rules about politeness... they have violated hospitality so badly that you owe them nothing.