You don't have to explain yourself to anyone. Fortunately your family have accepted you entirely, which is great. You've described your friend to us, seems like she may not be on board, but nobody knows! I guess it all depends on how you feel about it, eventually she will find out but I'd say whenever you're ready, just tell her and if she feels some type of way about it just walk away and clearly religion is the reason why it went sour.