My great-uncle is baptist and his wife is jewish. I'm sure there were some conflicts when they first got together, but they've been married for years and years and have 3 adult children. They worked together with their religions and compromised. They didn't raise their children as just baptist or just jewish, they meshed the two. If this girl is as crazy about you as you are about her then maybe when you guys get really serious and start talking about marriage, she can be accepting of you and your beliefs. Two different religious backgrounds can work, she'll just have to accept that you don't believe the same thing she does, and that not believing in anything in particular doesn't make you a bad person.