I have been happily married for almost 6 years. Recently, my wife had a miscarriage. Lately, she's had major problems with her self-esteem. She has said she's a failure, fat, stupid, and ugly. She has also said that I would be better off if I divorced her, which I have no intention of doing. No matter what I say to her, it never seems to be the right thing. I just don't know how to help her.
I don't need to tell you what's going on. She is grieving. Grief is like a broken bone. It hurts. It takes time to heal. If all goes well, it becomes a memory, one that stays with you for life. With a bit of luck the pain helps you to learn some lessons. In the case of emotional pain, these lessons can lead to growth in wisdom, compassion and maturity.
However, the reaction you described seems to involve more. Her loss may have triggered her emotional reactions to earlier losses, so in addition to grieving for this unborn child, she may also be grieving for someone she loved. At the time, she will have used some method of avoidance to relieve the pain, so that it is still with her, although buried. Further, her early life experiences probably made her feel bad about herself: some version of "I'm never good enough". This is the seed of depression, which has been activated by her ongoing sad mood.
As you know by now, one cannot argue with such feelings. This is because they are based on deeply held inner beliefs that may have been with her for so long that she's never put them into words.
She has a choice right now. She can choose to believe these inner feelings and act as if they were true, or she can simply put up with them, and ask herself, "Where do I want my life to go? If I could design my future, how would I be acting in it?" Then she can act in accordance with the answer.
It is perfectly OK to grieve for a lost child, whether born or not. It is also OK to acknowledge a past loss that was too painful to cope with at the time. When she can accept her feelings and that your love for her is OK and can be accepted - regardless of how she feels inside - then she can move on.
Love to both of you,