My husband would say," been there, done that"
. Fortunately, for us it worked out, but we would NEVER recommend it to anyone, unless you are game for conversion and realize the extent to which you would then become a different person - you are required to put on a NEW PERSONALITY, and you may find it doesn't really suit you eventually..
Although if she has dated you, and is even considering marrying an unbeliever - there is an outside chance that she doesn't put her full trust in the organization that she is a part of. The religion is a "WAY OF LIFE" , not just a go to church on Xmas and Easter deal - I would fully discuss this matter and see where she stands NOW, not later.
Best to you,
4JWY