Pocahontas was a native american woman living during colonial times.
When Supergirl read up on Pocahontas, she decided to go back through time and meet her for herself. Pocahontas had laid her head upon an Englishman, one of her tribe's captives, to prevent his execution. For this, she was to be executed herself, and prayed to her god, Manitou. Supergirl intervened and saved her life, later appearing as Pocahontas' spirit to convince the people that Manitou wished the girl's survival. ("Supergirl's Three Time Trips!")
At the Midvale Charity Ball in 1963, which was a costume party, Supergirl went as Pocahontas, to avoid wearing a flashy superhero costume which could draw attention to herself. ("The Girl who was Supergirl's Double!")