Who is Princess Bitterblue, later Queen Bitterblue of Monsea from Graceling and what is their importance?

Princess Bitterblue is the eleven-year-old daughter of King Leck of Monsea and his wife Ashen. When King Leck targets his daughter for abuse and torture, she flees with her mother. Bitterblue is eventually found by Katsa and Po, though her mother Ashen is killed. She develops under Katsa's influence, and she disguises herself as a boy along to get onto a ship to Lienid. Katsa later teaches the girl how to handle a knife and defend herself. In the end, Bitterblue returns to Monsea and is crowned Queen.