Pretty much everything Domus said. Those options might not work for every case, but they have helped a considerable amount of people before. If she has some underlying mental disorders (It doesn't sound like it, but that isn't something a few people posting on a forum can decide) then it will only be a temporary solution, if it helps at all. I can attest to sleep being a VERY big contributing factor to a person's mood, though I personally can't recommend any solutions if she does have bad sleeping habits. My sleep issues were solved by medication, but that doesn't mean hers will or should be.
Exercise has helped a lot of people with depression, and it could help improve her self-esteem. The only problem is time and motivation; It doesn't have to take a lot of time, but it sounds like that's your biggest dilemma for the moment. Explore your options and see if you can figure something out. Even a walk around a few blocks of the neighborhood could help, and it might be an easier transition for her to start with something smaller. Even better if there's a park or somewhere scenic nearby that you can use. Probably should of said it earlier, but it'd be best if you did it with her, telling her to do it on her own will only make it more difficult.
Seeing a psychiatrist or therapist may help to some degree, but aside from your financial/insurance situation, I want to say that it's not as easy as "going there, getting better". It takes time to find out what the problem really is. Sometimes your psychiatrist/therapist isn't really that great at their job. Sometimes recent events mask your true problems. It could take a lot of time, and a lot of trial and error before any real improvement begins to happen. And sometimes, it just plain doesn't work for some people. I'm not saying this to ward you away from it, in fact I whole-heartedly endorse it. You just need to keep the situation in mind, and use some common sense. Mistakes will be made, but that's just a part of dealing with life.
If you don't mind me asking, what country do you live in? I'm pretty sure the US has at least a few programs for helping people in need of mental care. I don't really know her situation, but are you sure she's not eligible for some kind of public or government funded health care? Might be something to look into if you haven't already.