Your mother in law unwell and is in the best place she can be. Most likely she is scared and lashing out at family. No. it isn't fair. Maybe she is also that an infection that is affecting her brain. Anti biotics may help. If your mother in law is going to be rude then take a break. You don't need it.

The family has done what is has needed to and you do not need to feel guilty. Taking care of yourself is just as important. Take time out to do something that will make you feel good. Maybe others have more ideas. Please be kind to yourself.