try writing her a letter how you feel, what you are assuming might be her problem, your willingness to listen, be nonjudgemental , and go to any extent to relive her of that which occupies her mind and just plain show her in small things daily that you are there to help or get help for her, not making her guilty or pointing out that you are helping her. help out with household and maybe either child might be having issues that flabbergasts her silently!. all the best
talk, listen, talk listen.....