I don't have Facebook, so I may not get it, but why respond at all? You have your beliefs and point of views and you share them on Facebook. Sometimes others will get offended but I think blocking or restricting them makes it seem like their views matter too you.
I would ignore her posts, like one ignores the comments on YouTube. If you really believe in your convictions, understand that you will be opposed, and just continue to stand by them and let her fling all the hate your way, it can't hurt you. You know you're right. Let her deal with the world on her own. If and when she and her spouse, your sibling, meet you at a family event, and she brings it up, re-state your views and talk to someone else.
If we really care about our beliefs, I think we shouldn't hide from those who oppose us. Ignore foolishness yes, hide no.
As an aside, of course her hateful words my actually hurt you, and it may make life easier to block or unfriend and that's o.k. But if you can take it, don't block her. I feel like that would be allowing her to silence you.