Complex sentence: After being held as a slave and concubine, she was one of a few captives ransomed by the Danish king nearly a decade later; after returning to Iceland she was sent to Denmark to relearn her Christian religion and her language.
Split into simpler sentences: After being held as a slave and concubine for nearly a decade, she was one of a few captives ransomed by the Danish king. She returned to Iceland, then was sent to Denmark to relearn her Christian religion and her language.