I wonder what happened with Charlotte's birth and if it was the nature of the birth that caused her disability.
We don't know the issue - perhaps celebral palsy?
The GP referred to a traumatic birth then he also said her depression was normal due to hormones.
In my mind that statement was a little odd.
If it was traumatic and something happened or a mistake made that caused the disability then that could very well be the reason for Kate's depression.
That would be situational not related to hormones or PND.