The canning process seals the air within the tin. When the soup contents are placed in the tin, it�s warm. As the temperature cools a minor vacuum occurs within the tin, thus preventing bacteria from developing.
Also, which is not very nice to know, certain preservatives may have been included to extend the shelf-life of the product. Finally, there is an additional process called irradiation, or �ionizing.� Using something that resembles the back of an old television picture tube, it points like a gun at the food and penetrates it, sterilising the contents. This protects the �chicken chunks� from deteriorating.
You can help your daughter do her own discovery process by looking at certain products in the supermarket. Bacon, for example is shrink-wrapped, thus removing the air and allowing it to have a longer shelf-life. And there are now many products that have gone through a combination of processes which eliminate the necessity of refrigeration.
Clearly, you have a precocious young lady in your midst! What a gift! I wish you very best regards.
Fr Bill