Kids grow up and parents need to accept it and grow up too.
My son's girlfriend is a Syrian Druze. Her family has completely different values and ideas from ours and it has been a challenge and learning experience for us with both positive and negative aspects, but we've tried to be warm and accepting.
Right now, my son and this gal have put the relationship on hold. Neither of them has ever dated anyone else and they have been going out almost 4 years and just turned 22. While my husband and I are encouraging them both to explore other friendships and relationships before committing, we know its not our decision to make.
Because my own mother-in-law was jealous, critical, and mean-spirited to me and her other daughter-in-laws, I went out of my way to be kind and supportive of this young woman. We all need all the love and acceptance we can get and the more you give, the more you get back.
My son and this gal may or may not have a future together, but it does not hurt anyone to offer as much kindness and support as you can.
I think the issue goes way beyond parenting and extends to how we treat all other humans. Do we offer them our respect, our understanding, and our compassion whenever we can? If we impose our own religion, church, and ideas on people, we drive them away and we ourselves fail to learn something different that might help us in our own lives.
The future is always a bit scary. I think this woman needs to look hard at her own fears and see that they are the main problem, not her son's bride to be.