“I just looked it up and apparently for people married before 1994 who were not Church of England or Jewish, the way they got married was at the registrar. Then they celebrated the marriage at a church ceremony.”
Not true. Most churches of all denominations are registered for legal marriages in the UK, and have been in living memory. Before 1837 only Quaker, C of E and Jewish weddings were legal - but there was no registrar option either. Notice has to be given at the register office for non CofE marriages, but not the ceremony itself.
Grandma might have a very big travel health insurance premium if she does come to the wedding in the US.
