It is great that your are supportive, I think if the friend is that triggering and won't listen and get help, you should back away. Let her know you will be there for her once she starts doing better (or relay it to her husband if you just can't talk to her) but that right now her actions are affecting you too much emotionally.

You've got your kids relying upon you, and if your friend triggers depression in you, I think for your childrens' sakes you should disengage for awhile. Even if not for your kids, just for yourself too.