PonkiePoo

If she makes a post on Facebook don't respond, just ignore it. I'd say do what Corgis said, make your own facebook account (a new one) that is separate from your one your mom has in contact with. Or just don't go on facebook if it makes you that upset. Perhaps anther option would be to use anther social media site.

As for the phone block her number if you can. Or just if she phones ignore it, pay no attention. 

Then avoid facebook, social media is one of the worst things if you have an opinion on something. I'd say avoid it, I find social media sites like that silly, and if they got to my that much, I'd just stop going on them. Since there is no reason keep hurting yourself by going back on there. 

Or blocking them like others have said could be an idea too. Or just ignoring them, since people are always going to disagree with you, especially religion.