Who is it you don't want contact with?
I don't see what religion has to do with contact with somebody. If somebody hurts you, no religion I know of says you have to put up with it. Is that what you're asking? Is it immoral? I'm not a christian, but I would not think any religion would think it's good to put up with abuse no matter who it came from.
How do you know what she says about you? I'm not sure who the "she" is though...your daughter or your mother.
I really like this motto and am learning to live by it:
"What you think of me is none of my business."
If this is your daughter again, it is probably best for your mental health not to read her FB or listen to her or even read her texts unless she can respect you. It is clearly making you very unhappy and you have the choice of going low to no contact.
You can't control what she tells her kids about you. You do have control about whether you let other people tell you what she says. You can tell them, "From now on, I don't want to hear anything ____ says. Please respect my boundary in this."
