I believe that you don't choose a religion, a religion chooses you.
Just started going to Universalist Unitarian myself. They seem to be Very Nice People. If anything, they aren't religious enough for me. No problem, I'll get my religiony stuff from having semi-paganish thoughts, and my human stuff from the UU's.
If your GF simply says "a Christian" without a denomiation (protestant, methodist, lutheran), then she's probably fundamentalist and they don't seem to compromise well.
It may help you to go to Beliefnet.com and take their quiz: Belief-O-Matic - Beliefnet.com
It's a website commited to help people to choosing a faith (or having a faith choose them?).
5'0" female, 44 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 111 on sugar cheat. Currently fighting off sugar/candy cravings with bulletproof cocoa and a little rice.
I (try to) follow by-the-book primal as advocated by Mark Sisson, except for whey powder and a bit of cream. I advocate a two-month strict adjustment for newbies. But everybody is different and should tweak Primal to their own needs.