Well even Doctor Ferguson was stumped on that one. Did she see herself as deep down virtuous rather than the Devil's Child her mother had painted her?
Maybe Dr.Ferguson wasn't up to speed with the variations which mental health could show itself. I wouldn't have gone as far as diagnosing schizophrenia myself,rather a personality disorder which the Madonna Complex covers a multitude of different problems. Narcissism for starters,where Sheila,when modelling,had to fit the part and constantly asked for reassurance. Short-term anorexia,which could have happened after the twins were born when she worried that she'd put on too much weight. Prior to that,her breast augmentation which proved that she wasn't happy with the way she'd looked.( I wonder who paid for that ? ) A high-maintenance girl which led her to her mental health problems.
To have openly admitted of having such a complex tells me that she knew what she was at,whereas having deeper problems such as schizophrenia a patient can't tell you what's wrong and most of the time they're in denial anyway.
Virtuous she wasn't,with her drug dabbling,etc. June would have had that quality which she was trying to project onto Sheila,but Sheila rebelled and went in opposite directions,but at the same time fighting with herself because of the control that her mother had over her.