My personal opinion is that if she really is a devout christian,
forget her.
Unless you can really accept it and convert, all the things that
christians do will continue to irritate you until one day you
cannot take it anymore.
However, it's mostly up to the couple.
My girlfriend is a christian. My girlfriend's parents are devout
christians. My girlfriend's dad probably could have a PhD in
Theology if he bothered to go get one.
However, my gf does not preach about christ to me and I don't
criticize christianity in front of her. Overall, it works out
pretty well.