If you had planned on having children in the future, ask her how she would feel if your son or daughter had sex with someone they dearly loved and were disfellowshipped, would she feel it was right to shun them? Or what if your child got baptized young and later didn't accept the religion, maybe because they could find no proof that the GB had been appointed by Jesus in 1919. How would she feel if she could never, ever have any communication with them?
Her answer will even help you to consider whether you really think this person will be the sort of mother that you would want for your children.