Is it permissible to eat food prepared by nuns in a school affiliated with them?

Food prepared by nuns or other People of the Book is permissible to consume, so long as it does not contain anything forbidden by Islamic law, such as carrion, blood, or pork. The food and slaughtered animals of the People of the Book are permissible for Muslims, as Allah Almighty says: "This day [all] good foods have been made lawful for you. And the food of those who were given the Scripture is lawful for you and your food is lawful for them." [Al-Ma'idah: 5].