In thinking more about your dilemma.... have you considered calling an ambulance for your MIL (preferably when partner is not in the house)? When emergency crew arrives and they see how emaciated and unwell she is, they will very likely transport her to hospital without delay. In hospital, social workers will get involved and ask questions about her home situation. With her out of the house, you will have the unique opportunity to extricate yourself from your situation with zero obligation.
With you out of the picture, your partner will have no choice but to assume his rightful responsibility. My guess is he can't or won't take care of her either, so a nursing home is the best option there is. There she'll get the medical attention she needs, be surrounded by carers 24/7 and enjoy the company of other elderly people like herself. You would be doing her a tremendous service and freeing yourself, as well.
What time do you get up and go to bed?
What were your dream names for your kids when you were growing up?


