"For where two or three are gathered together in my name, there am I in the midst of them."
- Matthew 18:20 (King James Ed.)

Church is defined by the church as the people. The building, pews, alter, these things are just things, the people is what matter and make church chuch. If you do like this girl and want to stay with her, you may satisfy her and go once. Get a feel for it, you may like it. If not you just explain that you don't like it. As said, honesty is the best policy. If she can't like you for who you are, she needs to leave.

I was raised in church, but once I got to a certain age it was my decision to go or not to, I stopped. I'd prefer to not say why, I just have my personal reasons. My GF is a believer but as I do, doesn't like to go to church. But on special holidays, Christmas, Thanksgiving, Grandmothers birthday, we surprise her and attend with her to her church. Gives us both a feeling of "good deeds" not for ourselves but for her. Some sacrifice is a good thing, but you can't change who you are and if you don't like it she needs to be able to understand that.

Her parents should understand too, as Christians we shouldn't FORCE religion onto those who don't accept it. Think of how her parents would feel if you practiced your lifestyle choice of Nudism at a family get-together. Just sayin.