One of our daughters suffers terribly with depression too, suppose it must be genetic as said before, I get it, and my mum was a chronic depressive in her earlier years.
Our daughter has found exercise is a great mind helper, she visits the gym almost daily, not to bulk up but to strengthen her core muscles after a chronic back problem due to lifting a patient, she is a midwife, her outlook has improved so much with the extra physical activity.
She still needs tablets to keep her serotonin levels up, but is way better than she was before.
Depression is an a