Tell her that she's thinking of mold.
Bacteria and viruses live everywhere, even in the extreme conditions of space; in fact, there are those that thrive and become more virulent in what we would consider unlivable conditions. Also, in inhospitable conditions, bacteria can become dormant until conditions improve (they're then referred to as spores). A bacterial spore on cold metal can wake up to happiness when one's face gets rubbed on it.