I think that it is important for her to see a doctor and to get counseling. Maybe even couples counseling, or counseling for you to be able to deal with her issues. Not that you should deal with her issues, but for you to be able to handle the situations that may arise. Understanding her moods and the way that she feels. Depression is no fun at all. Though it seems that people who are depressed want to fight, they really don't. They just don't know how to express themselves and everything comes out all messed up from holding it in for so long.
I am going to post a site that maybe you can get her to go to. It is totally free.
http://www.moodgym.anu.edu.au/welcome
I don't know if she will be interested or not, but she might. If she doesn't, it is so important that she talks to a doctor or a psychiatrist to help her deal with her depression. All you can do is encourage her to do the right thing. This is not something that you can fix. But be there for her. Try to help her, but don't tell her what to do.
I hope that I have helped in some small way. I am not a doctor or a professional in any nature. But I have lived with depression for many years. I manage mine with medications and counseling. I have been in remission for a long time. I am pretty happy for the most part. But that is what worked for me.
I hope that you are having a better day and that your wife is feeling well.
Hugs, Karen