Sometimes it is. Common Sense is not so very different from "Conventional Wisdom". (It's different, but not completely.)
This researcher used the classical scientific method. She made observations, developed a hypothesis, (a theory if you will) and then made predictions as to the outcome of those experiments.
The problem with "Personal observations" is that they are necessarily limited to everyday situations, and observable factors. Try coming up with Special Relativity using "common sense based on personal experience and observation".
How do you explain her results if the virus was not causing the increase in fat cells under very controlled conditions, were overeating was not a factor, and the baboons were what they were, from a "moving less" standpoint, before and after the infection?