How can I help my partner with her depression??

I have been with my partner for just over a year, she has been suffering from depression for nearly six years now as her mother died when she was 17 of breast cancer. Two years later she lost her nan (her fathers mother) through cancer also. Her living grandparents have never been very sensitive towards her and her father has never wanted anything to do with her or her siblings. Since I have known her she has had two mini breakdowns and is now trying to get some help. I am at a loss as what I can do as everything I do seems to be the wrong thing, she takes everything out on me and all that goes wrong is my fault. We are having a few problems in our relationship due to these issues and I dont want to lose her. Can anyone help??