She's Killin Me Here ... Could Use Some Tips on Living With the Elderly

First take care of yourself- this is NOT being selfish. You need good sleep& nutrition. You two should each take turns at night to take care of her if needed so that one of you will get a good nights sleep.

As for your Mother in law, she may need some medical attention or at least maybe something to help her sleep- at the least she sounds sleep deprived & depressed too. So take her to the doctor. We could have a long discussion about doctors but you'll need to make sure they give "real" help (for example every time I have sinus infection they tell me it's allergies & I have to be bit of a jerk to get antibiotics).