Poor Mirabella. Sure, the girl made some mistakes in her time, but boy is she paying for them. Forced to ride all over the world trying to help the same number of knights she killed by disdaining her love, she is whipped and mocked by her unsavory escorts, Disdain and Scorn, along the way.
Mirabella serves as a warning for women in general to not be too proud or disdainful. Apparently in Faerie Land, playing hard-to-get will kill a bunch of love-struck young men. Mirabella is a fitting victim for us to encounter in the book of courtesy, since her unwillingness to politely entertain or acknowledge the courtship of men is the epitome of discourteous behavior—notice again the root word "court" that connects both concepts.