vittvin,
I just went through this almost as you are about to. My daughter was married two weeks ago. About three months before the wedding she sent me a letter telling me I was not invited to her wedding, nor was I to meet her husband to be, nor call her again. She does allow me to contact her via email and letters, thankfully. She told me in her letter that her new hubby-to-be was currently shunning two of his own disfellowshipped brothers. I feel certain it was his influence on her which made her take the final stand.
If your new son-in-law-to-be is a hardliner, he may do the same to your daughter. Remember, the man makes the final decisions! If she will marry him regardless, why does she need to know today? If your news will not change her mind on the marriage, then why bother? You will be shunned soon enough; sadly enough.
My personal opinion and hope you find your way peacefully.
Bryan