It doesn't matter what SHE thinks (or anyone else). you have established your belief/boundaries.

She needs to RESPECT that. If not, you could tell her (respectfully of course), that you will not discuss it with her.

How would she feel if a muslim/jew, etc., etc....tried to convert her??!! Mention that. What would I say to her if she brought it up ever again?

This (subject) is NOT up for discussion, mention or debate. If you CHOOSE to persist, we cannot have a conversation.

DISENGAGE. You have quickly, succinctly and politely given her your boundaries. What she does with that information....is her choice.........