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

Bitterblue is the eleven-year-old daughter of King Leck of Monsea and his wife Ashen, the aunt of Prince Po of Lienid. When King Leck targets Bitterblue for abuse and torture, she flees with her mother. Bitterblue escapes and hides and is found by Katsa and Po, though her mother Ashen is killed. Bitterblue develops under the influence of Katsa, who saves her life. Bitterblue disguises herself as a boy along with Katsa in order to board a ship to Lienid. There Bitterblue learns from Katsa how to handle a knife and defend herself. After King Leck's death, Bitterblue returns to Monsea and is crowned Queen of Monsea.