Leave her alone my brother. This could cause a chain reaction with her line of thinking. She may really need what she has. She may get crazy on you. Keep low on this... let her work it out.

If the only thing keeping her in line is her pretend man in the sky. Understand at her core, she is a bitch.

Ask her if she's willing to put up with the way others will begin to treat her if she starts acting like an asshole.

I told one of my friends that i was a atheist and she told me i couldn't be, because i wasa good person. I worked at Sears for 15 years and i was the one responsible for the can drive, toy drive, and for school supplies for teachers. I also donate blood and volunteer for meals on wheels and work in their kitchen. Just because i don't believe in god doesn't mean I'm not a good person and try to make the world a better place. I don't completely understand the because i know many Christians who are only Christians in church. As soon as they leave they are only out for themselves! Not all, but many.

"If God didn't exist, I will have no reason to be kind. I will do everything to get even if someone wronged me"

I would have responded to that as "So, you're saying I'm a heartless vindictive ass?"

The kindest, most empathic people I have met have been agnostic or atheist. The most immoral people I have met have been fundamentalist Christians/Muslims.

I think I would engage her further in discussion, telling her how you still feel even without a belief in God that you have a responsibility to others and to yourself to be kind and just. And maybe tell her you don't think she's giving herself enough credit for what sort of person she'd be without belief, because you don't think she's deep down the sort of person to hurt others who refrains from doing so only because of a fear of God's judgement and punishment. Let her know you believe in her goodness, and tell her that the many religions, as varying as they are, have a common thread of goodness in them, though often perverted by power systems, and this hints to a common decency. Our species created religion because we're looking for goodness, but such formal structures can mislead us and convince us that our nature is evil. But goodness is innate to us, except in extreme sociopathy and psychopathy. We also have selfishness and anger and other traits we see as negative, and that's what humanity stands against in religion. Ask her if deep down she really wants to hurt people. Does she honestly think the only reason she doesn't murder people or steal from the needy or cheat on you is because she fears God's punishment? I'm guessing if she's honest about it, she doesn't want to be a murderer or a thief or disloyal. She doesn't actually believe those are positive characteristics in the absence of an authoritarian disciplinarian.