I don’t remember the backstory. Does the SIL have a husband or is she completely dependent on you financially? It looks like she has frustrations in life which she is taking out on you. It is not fair to you as you realize and you are spoiling your own health and peace of mind. Will your husband agree to go to a counselor with you so you can get some strategies on how to deal with the situation? If he sees from a third party how badly this is affecting you it might inspire some changes.