How to forgive my Mother?

Tell your sister why you want NOTHING to do with your mother. Tell your mother that she WON'T be staying at your home. IF she shows up anyway, DON'T allow her to even set foot in your home. Lots of people will tell you to overlook your mom's "problems". DON'T. You are responsible for your actions. I'm responsible for my actions. And, your mother is just as responsible for her actions. It IS sad, but to HELL with your mom.