Dr. Jones says that she has a hypothetical explanation about the relationship between the ingestion of caffeine and the experience of anxiety. Which term would BEST describe Dr. Jones's hypothesis?

Her hypothesis is a theory

Explanation:

A theory refers to an explanation or hypothesis that is intended to explain something based on the general principles independent of the thing being explained therefore it simply a speculation hence it is unsubstantiated.

Dr. Jones has hypothetical explanation but it has not been tested to determine the relationship between ingestion of caffeine and anxiety. So its is simply a speculation making his hypothesis theory.