She doesn't want him to know
I believe that this is Personification because she's giving nonliving traits human characteristics.
Photosynthesis produces oxygen and glucose mainly. The oxygen gets released into the air, because oxygen to plants is like carbon dioxide to us. It doesnt harm them, but they cant use it. The glucose ends up either being used by the plant or stored somewhere within the plant to be used later.
Explanation:
Through three cheese trees three free fleas flew. While these fleas flew, freezy breeze blew. Freezy breeze made these three trees freeze. Freezy trees made these trees' cheese freeze. That's what made these three free fleas sneeze.