Maybe she takes her religion seriously, she loves you, and she is concerned about where you stand with God.
I don't know what kind of church she attends or what her religion is; I've discovered that even among the Christian religion, there are so many different beliefs and customs among them. I realize that church is a benign social gathering for some churches; it resembles a lot of other social gathering one might have in the community; they have dinner, activities, and so on, but Jesus is the topic as opposed to something else.
Some people, however, take serving God very seriously, and there is the issue of what happens after death. If she feels she must make an effort to have favor with God, she must be concerned if you do not. I would think that wanting only good things for those we love is a normal feeling. After all, just because someone chooses not to attend church or put God first in their life, that doesn't give them a pass in the heart of the believers, especially if it is someone they love and care about.
There is nothing more sad or glorious than generations changing hands- John Mellencamp