A chance to both test her potential husband as well as to show herself in a good light. If it's her, she definitely won't let that chance slip by.
If they do get married in the end, this will become a heroic tale of how they rescued a slave from a criminal.
And in the distant future, her name will be carried on as the wife of the virtuous Hero who defeated the evil Hero.
Shit! This trash king and bitch princess!
No, wait... the princess, a bitch...?