I'm guessing that over 99% of the people who have gender identity disorder actually suffer from some other form of mental illness.
It almost always occurs in the presence of spectrum disorders or personality disorder, mainly borderline personality disorder. Sometimes it can be a psychotic delusion, but we have medicines for psychosis.
I have trouble with even letting adults make their own medical diagnosis sometimes. They obviously have mental issues. There is a thing were some people think that a part of their body (usually a limb) doesn't belong to them. A doctor in England amputated a limb from two people before the government stopped him (no fines or anything).
The doctor was upset as he had two other patients waiting for the procedure, and he wanted to give them the relief they so desired.
A divorce was part of the background for this atrocity.
I wonder if her mother approved of the atrocity and her father opposed it.