Marriage is hard work and throw in the type of stress and loss and hardships that you and your wife have had to face these past years makes it even harder. It might not be you or your marriage that your wife is upset over, but her life in general.
Most of the posters on this board have spouses that were cheating, abusing drugs, or alcohol, gambling issues etc. Not all of our perspectives or experiences will necessarily apply to you or situation.
Your wife is not one of these cheating, lying, abusive spouses. She is a spouse in need of support, affection, love, and loyalty. She is a spouse that (like you) has had to endure the greatest suffering one could possibly endure and is having trouble coping.
Have you tried one of the DB counselors? I found mine helpful and feel that had I used mine earlier in our situation our marriage could have been saved. Much of her advise was actually not what was recommended by many posters on these boards. She recommended cultivating a friendship instead of going dark.