I have an aunt who is permanently out of my life. Even when I have to be in the same place as her, I will no longer interact with her in any way. She has always been awful, and then her behaviour at my grandmother's memorial was so atrocious that I decided that I wanted nothing more to do with the woman, so I have decided that I will simply behave as if she doesn't exist.
I found it amazingly liberating to realize that even if I share genetics with someone, I don't have to put up with their crap. If this relative is nasty to you, it's on them to shape up, not your responsibility to suck it up and be nice to someone who's horrible.