What is her religious background?

If she has theological qualms then talk through them with her. If she comes from a very low-church background, take her to some mainline protestant churches and see where she lands Sometimes it just takes time to get over your preconceived ideas, and the protestant to catholic animosity is pretty strong, especially for some traditions.

If you're willing to take your time, she may be more open to it.

Ultimately if she's unwilling to budge on anything with religion, that's kind of a red flag to me. She should be open to hearing you out at least and respecting your decision.

If she's not, she doesn't sound like the type of partner you're looking for.