Although, to me, it sounds less like she's quit being a Christian and more like she's embracing this guy's philosophy:
Which seems pretty Christian to me. Or at least, the definition of being Christian that the lovely, lovely Jesus freaks from David Levithan's Wide Awake¹ adhere to. I mean, as long as she doesn't go full circle and start hating on the people who don't agree with her opinions and beliefs.
¹Which, yeah, I had some issues with, but I did love the Jesus freaks.