Final answer:
Wendy is the one experiencing a stress-induced stomachache, as her symptoms occur in response to stressful situations with her father, indicating a link between her stress and digestive discomfort.
Step-by-step explanation:
The person who has a stress-induced stomachache among the options provided would be Wendy. She experiences stomachaches every time she has to talk to her strict dad, indicating that her stomachaches are triggered by anxiety and stress. While Tim's and Lisa's stomachaches seem to be related to food intolerance and possible side effects of medication or recent illness respectively, Wendy's symptoms are closely tied to stressful interactions, aligning with the concept of functional dyspepsia or indigestion related to stress. Stress can lead to functional dyspepsia, which affects the digestive system and is commonly associated with stomachaches without an organic cause. Symptoms of stress-related digestive issues can include upper abdominal pain, belching, and nausea, which are a result of the body's response to anxiety.