The Two Princesses of Bamarre (The Two Princesses of Bamarre, #1)

The Two Princesses of Bamarre is a 2001 novel by Gail Carson Levine, the author of Ella Enchanted and several other books. The story revolves around the lives of two sisters who are very close, but as different as night and day. When one of them falls victim to a deadly disease sweeping the kingdom, the other must find her inner strength and bravery to discover the cure, and save her elder sister.