Answer:
Jennifer's conclusion might be incorrect because she might have got nausea from eating something else. Therefore, other things may be responsible for her nausea and not Asparagus. :)
Answer:
In order to conclude her test she should try fasting. She should avoid eating other things for a specific amount of time and after that only take Asparagus. If she feel nausea again then it can be concluded that nausea is being caused by asparagus otherwise she can conclude that Asparagus doesn't cause nausea.