Marcie and the God Squad - Breaking Free

My kids attend public school.  That's by choice.  So I was a little surprised to hear about this recent encounter Marcie had with some "friends" (and, yes, I guess I use that word lightly).  The interaction went something like this:

Marcie: "Church can be so boring sometimes."

Girl A: "That's not nice to say."

Marcie: "But it's the truth."  (in her head- "at least at my church.")

Girl B: "You should be grateful for all the things you have-- God has given us a lot. [and on and on and on about how great God is and how ungrateful Marcie must be if she thinks church is boring.]"

Marcie:  "It's my opinion.  I'm entitled to my opinion."

Girl A: "I can't believe you don't believe in God!"

Marcie: "I didn't say I don't believe in God!"

I'm not sure if the atheism allegation arose- in Marcie's original telling, it did.  In subsequent tellings she focused more on the first part of the interaction.  In every telling, though, Marcie decided to just walk away.

So she left the group of girls for a bit.  Then she decided she should go "talk it out."  (That's how she described it.)  And back she went.  And when she returned, the other girls told her that she wasn't really welcome.  You know, because of her beliefs. 

And then I showed up to take Marcie home.

It's been bothering me for a while now.  I'm not thrilled about the way I see this group of second grade girls treat each other.  They are not particularly kind.  There is, from my perspective, a ring leader-- though I admit I'm not there day in and day out to observe it.  And I don't know how to help Marcie just. walk. away.  And I mean permanently.  If you are spending your days with a group of girls who build themselves up by putting other people down, it will never be a healthy relationship.  So why does she keep going back?  How do I help her break away?

Any ideas?

[As a side note, why are second-graders engaging in such religious marginalization?]