Over the past decade+ I've also found that an ability to monitor and hack your own mood is an incredibly valuable skill. Know what things trigger depression and either avoid them or work out a contingency plan to weather the storm... Have a mind-killer available for when a spiral is coming and force yourself to use it.
This is basically exactly what I've been working on to overcome my own depression.
Reading Less Wrong and working on the basic techniques of the sequences has made a huge difference. And note that the "mind-killer" doesn't have to be a particularly healthy behavior - it just has to be better than the depression (at least to start on).
It sounds like your girlfriend is dealing with some heavy external stuff, in addition to chemical brain stuff. I've found it helpful to remind myself that that which can be destroyed by the truth should be, but the reverse is also true. For me, being able to feel the difference gives me huge leverage on eliminating the irrational kind.
My girlfriend suffers serious depression. She has sleep disorder, anorexia, chronic pain, problems to concentrate, low selfesteem, daily low mood, listlessness and is very indecisive. On the other side she considers herself very happy apart from the "depression periods" and we have a great time together. We already consulted a psychotherapist, but there is waiting time about one month. I buyed her fishoil capsules, because she eats no fish and there is mild evidence that it helps treating depression (I don't think this will affect her depression greatly, but fishoil seems like an overall good idea). We often go on walks to catch some sunlight and get her some exercise.
She says she never want's to take antidepressants because she fears to get dependent from them. I think she might change her mind if there are very good arguments in favour of them. She is quite rational in spite of not knowing the LW-stuff. Does anybody of you know if there is any information of the succes rate of medicamentous (and psycho therapeutic) treatment available?
I highly appreciate any advice.
Furthermore i want to call attention to the topic of depression. A huge share of the population suffers at least once in their lifetime under depression (~20% in Germany). Sadly it's often not taken serious and a big taboo to speak about. Many people see it as self-inflicted. My girlfriend's mother doesn't believe in depression as a disease (see diseased thinking). It's a paradigm of irrationality that hurts people.