In my opinion depression doesn't always need a trigger. For me it most often comes for no reason at all. Therapist tend not to believe in a biological basis it seems. I tend to come up with triggers just because I am baffled as to how it happened and they may have had nothing to do with it. It could be the damn alignment of the moon and venus for all I know. Mine has traditionally been very seasonal and three or four times a years things go whacko.

If there is no obvious trigger tell her my genes decided to flip on me and it is biological and no one knows the answer.