Wow! THAT is a great question. Why did she need a passport?
Why did she need a passport, at age 17 and “living in Hawaii”?
Perhaps to cross the border from Washington State into Canada - to give birth to the thus non-US citizen baby Barry...
and to then return to the US 3 weeks later, to attend the University of Washington in Seattle - and visit her high school chum on Mercer Island.
MayIt has been speculated that the Dunhams’ Little Red Unitarian Church went on a “friendship tour” of Comrade Fidel’s Cuba around that time.