Joseph, how about a Sefardi girl who grew up in America, in an Ashkenazi Beis Ya’akov who is ready to follow Ashkenazi minhagim if the husbans is an Ashkenazi who gets rejected out off hand because she’s Sefardi?
Generally speaking, if both spouses have middos tovos it can work out even if they come from different backgrounds. If they don’t have the middos, then even if they are from totally the same background, there will be problems.
Also, Joe, a most important principle: if there is room in the heart, there is room in the house.