She won't get an email but it will appear in her
MDE.
She would have to go looking for it, though. If she doesn't regularly look at MDE when there's no trip planned, you'll be okay up until a certain point--I don't know exactly when that is--but before the trip she may start getting push notices if she allows them on her MDE app.
AFAIK, there's no way to prevent this. And a trip to WDW is wonderful even without the surprise part.