Does she know you are asatru, or are you rusing her? If you are rusing her, you need to stop.
Now that said, remember the the nature of women. Once you sleep with her and/or prove your worth and/or get some kind of commitment, she will generally accept everything about you and change herself to accommodate. So that shouldn't be an issue. Even if she still wants to be a Christian, she will soften her views and accommodate your worldview, provided she is sane.
The real challenge will be dealing with her kin, and you'll have to figure out if you're up to that. Most Christians around here are borderline retarded, and I'm not sure I'd want them coming over every holiday and shitting all over the place.