Assumption one: The de-friending was on purpose.
Maybe, maybe not. I have accidentally de-friended people with a slip of the mouse-click, without noticing. It's possible.
Assumption two: The de-friending was from dislike, disapproval, or malice.
Sometimes people get too caught up in their Facebooking and decide they need to take a break, pull back, exercise some discipline. A relative of mine did de-friended everyone except her children and grandchildren, because she realized she was spending way too much time on Facebook.
Assumption three: The reason for the de-friending has to do with religion, or with the link you posted to your journal here.
She might have a different reason altogether for de-friending. Maybe you posted or said something she interpreted as hurtful or insensitive that had nothing to do with religion.
It wouldn't hurt to communicate with her, saying something to the effect of "I notice you de-friended me on Facebook, and I was hoping you'd tell me why."
If she writes back something to the effect of "Please don't take it personally, I'm etc.etc.etc...." or even "What? I de-friended you? OOPS! Fixed!" you're fine.
If she writes back something to the effect of "I was really hurt by what you said about xxxxxxxxxx, and I don't feel comfortable sharing Facebook with you" you can at least address xxxxxxxxxxx, maybe start a dialog and repair the damage.
If she writes back "Yer goin' to hell and I don't wanna be dragged in your wake" you know you're well out of the relationship.
If she ignores you, you haven't lost anything, you're right where you are now.
helpfully,
Bright