YOu can do a few things.
You don't have to invite her. Period. IF she asks, you tell it to her straight. Everyone is tired of her language and polictics. No one else brings it up. You have asked her repeatedly to not to do so and she still does. You will not bow down in you own home any longer.
If she starts up, you must speak up and tell her to stop. Repeatedly if you must. If you have to, show her the door.
When she starts in, everyone, and I mean, everyone, (so they would have to be in on it, except for those that you think would tattle to sis), stop what they are doing, whether eating or talking and just stare at her, silently, with the death stare. If she wants to be the center of attention, give it to her. If you have to, keep doing this every time she starts in. And then when she stops, everyone start talking again, but not to her. I would ignore her.
or last and not least,
tell her before hand to limit her language and there will be no talk of politics. If she does, she will be asked to leave.
you could discuss politics with her, stick to your guns, etc., especially those that differ and keep at it until she gets so mad she leaves on her own.