Depression can have pin-point causes (and usually it does) but sometimes it is just an amalgamation of different stressors which just get on top of you. Your friend certainly needs some help and support from what you are saying but there is only a limited amount of help you can give her. If she is not prepared to fight herself, then much of the energy you invest will be in vain. All you can really do is be there for her when she needs you. As for pin-point causes making depression less depressing... its not a theory I buy into.