1. Most Europeans have Jewish ancestry. Intermarriage and going off the derekh were not invented in the 21st century. It would not be a hiddush if Ivanka (or most Europeans) began life as a safek Jew. This is an argument against using a Shabbos goy (unless they are from an ethnic group with little contact with Jews).
2. If a ger is joining a modern orthodox community, one should assume they will act similar to that community.