When do you "defriend" someone?

What would cause you to stop talking to someone?
I’ve been having some problems lately with a “friend” of mine, and I’m trying to make sure that these reasons are good enough to leave the entire situation behind me.

This girl moved to Arkansas from Idaho to marry her now husband. But she posts a lot of things on facebook about how terrible it is here, how everyone is racist and homophobic, etc. How Idaho is so much better, yadda yadda yadda. Not like that wasn’t enough to upset me, but this girl is “artsy”. I’ve shown her a few cultural appreciation websites, and instead of learning a lesson from them… shes taken to taking photos of herself in black face and rainbow war paint.
Oh its giving me acid reflux. How do you cut someone like this out of your life? Surely these are good reasons, right?

I just need that extra little push to do it. I don’t think I’ll regret this, but wow is it stressing me out.