I assume she's very religious as well. Otherwise she could just ignore it, and later marry a man who is not concerned with such matters either, right? Especially since being "a bastard" by religious law is not such a big deal in a secular state like the US (is it?)

The whole situation seems extremely weird to me. If they are both serious about their religion she has no sway whatsoever. She can either wait for him to change his mind, or for the whole get-tradition canceled. Which can take forever.