Prior to around 2000 Esther Crawley did biological research. After a break of a year or two with no research, she started doing CF/CFS stuff. As far as I can tell she doesn't have a theory about ME/CFS pathology, but she does believe that CBT/GET can cure it. She actually hasn't done a lot of research until the past year, and most of it is a bunch of fluff - playing around with questionnaires, rates of chronic fatigue in teens, etc.
Reports of her re-diagnosing children with Pervasive Refusal Syndrome if they don't get cured by CBT/GET would suggest that she views the symptoms of ME/CFS as being entirely psychosomatic. She also omits PEM, or dilutes it to post-exertional fatigue, which would suggest she doesn't believe specific symptoms are important, which is also an indication of a psychosomatic viewpoint.
She doesn't seem very intelligent, and I doubt she has a well-developed theory which she could express in a coherent manner.