There's some doubt. Whether you give your friend the benefit of that doubt is up to you.
Consider the obvious: your friend knows you don't even believe there is a Hell, so might simply be joking in a way she thinks won't offend you or the Christian. Just working from this one anecdote, I can't confirm definite enemy action here. You never know, she might regret saying it after thinking about it.
Do think about asking her directly whether your atheism is a problem. You might well avoid a whole bunch of Seinfeld-style conversations where the one important thing is never stated. She is still ostensibly your friend. If there is a problem, maybe you can work it out, perhaps by dispelling a myth or two about self-declared atheists.
As for your Christian, my heart goes out to you. That was one sadistic sentiment about laughing while you burn, even if she does actually have a god behind her. Holy schadenfreude, Batman.