It is time for the post-partum depression rant.
Common wisdom is that post-partum depression is unrelated to any underlying emotional issues, and is purely caused by the chemical and hormonal shifts of birth. Thus, nobody ever goes to therapy for it and only takes drugs.
This is completely proven false. Data shows that women who just gave birth are no more likely to suffer from depression than woman of similar ages who did not just give birth. This conclusively proves that it is not related to the hormonal changes of birth.
Rather, women who are prone to depression, and get depressed at other times, also get depressed after giving birth. Probably because of the emotions attached to giving birth, which trigger the underlying emotional issue.
They should go to therapy, and if the therapist says it is all hormonal, they should find a new therapist.