This is a tough situation. If everything is as you say...I would send her this post, written by hand. It is eloquent and sincere.You must be there for the kids of course, and try to give them a semblance of normality.
Remember that she is suffering and she might be avoiding contact because she feels guilty about her inability to overcome her maladies.
Depression is foremost a lack of hope. Hope for the future, hope for a better tomorrow. It is a devastating disease. Be there for her.