Final answer:
Sheila's response to spoiled milk is an example of taste aversion, where her brain has conditioned her to feel nauseated by milk after a bad experience.
Step-by-step explanation:
The scenario described best demonstrates a psychological phenomenon known as taste aversion, which is a type of conditioning. In Sheila's case, the experience of ingesting spoiled milk (the conditioned stimulus) and feeling nauseous (the unconditioned stimulus) has led her to develop a strong aversion to milk at the mere sight or smell of it. Taste aversion is a survival mechanism, where the brain creates an aversion to foods that have previously been associated with illness or discomfort, to prevent future harm.